Merge, join, and concatenate.ipynb

{
 "cells": [
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "# Merge, join and concatenate\n",
    "\n",
    "This is daru translated version of http://pandas.pydata.org/pandas-docs/stable/merging.html"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 1,
   "metadata": {
    "collapsed": false
   },
   "outputs": [
    {
     "data": {
      "text/plain": [
       "true"
      ]
     },
     "execution_count": 1,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "require 'daru'"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## Concatenating objects"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 2,
   "metadata": {
    "collapsed": false
   },
   "outputs": [
    {
     "data": {
      "text/html": [
       "<table>\n",
       "  <tr>\n",
       "    <th colspan='5'>Daru::DataFrame(12x4)</th>\n",
       "  </tr>\n",
       "\n",
       "  \n",
       "    <tr>\n",
       "      <th></th>\n",
       "      \n",
       "        <th>A</th>\n",
       "      \n",
       "        <th>B</th>\n",
       "      \n",
       "        <th>C</th>\n",
       "      \n",
       "        <th>D</th>\n",
       "      \n",
       "    </tr>\n",
       "  \n",
       "\n",
       "  \n",
       "    <tr>\n",
       "      <td>0</td>\n",
       "      \n",
       "        <td>A0</td>\n",
       "      \n",
       "        <td>B0</td>\n",
       "      \n",
       "        <td>C0</td>\n",
       "      \n",
       "        <td>D0</td>\n",
       "      \n",
       "    </tr>\n",
       "  \n",
       "    <tr>\n",
       "      <td>1</td>\n",
       "      \n",
       "        <td>A1</td>\n",
       "      \n",
       "        <td>B1</td>\n",
       "      \n",
       "        <td>C1</td>\n",
       "      \n",
       "        <td>D1</td>\n",
       "      \n",
       "    </tr>\n",
       "  \n",
       "    <tr>\n",
       "      <td>2</td>\n",
       "      \n",
       "        <td>A2</td>\n",
       "      \n",
       "        <td>B2</td>\n",
       "      \n",
       "        <td>C2</td>\n",
       "      \n",
       "        <td>D2</td>\n",
       "      \n",
       "    </tr>\n",
       "  \n",
       "    <tr>\n",
       "      <td>3</td>\n",
       "      \n",
       "        <td>A3</td>\n",
       "      \n",
       "        <td>B3</td>\n",
       "      \n",
       "        <td>C3</td>\n",
       "      \n",
       "        <td>D3</td>\n",
       "      \n",
       "    </tr>\n",
       "  \n",
       "    <tr>\n",
       "      <td>4</td>\n",
       "      \n",
       "        <td>A4</td>\n",
       "      \n",
       "        <td>B4</td>\n",
       "      \n",
       "        <td>C4</td>\n",
       "      \n",
       "        <td>D4</td>\n",
       "      \n",
       "    </tr>\n",
       "  \n",
       "    <tr>\n",
       "      <td>5</td>\n",
       "      \n",
       "        <td>A5</td>\n",
       "      \n",
       "        <td>B5</td>\n",
       "      \n",
       "        <td>C5</td>\n",
       "      \n",
       "        <td>D5</td>\n",
       "      \n",
       "    </tr>\n",
       "  \n",
       "    <tr>\n",
       "      <td>6</td>\n",
       "      \n",
       "        <td>A6</td>\n",
       "      \n",
       "        <td>B6</td>\n",
       "      \n",
       "        <td>C6</td>\n",
       "      \n",
       "        <td>D6</td>\n",
       "      \n",
       "    </tr>\n",
       "  \n",
       "    <tr>\n",
       "      <td>7</td>\n",
       "      \n",
       "        <td>A7</td>\n",
       "      \n",
       "        <td>B7</td>\n",
       "      \n",
       "        <td>C7</td>\n",
       "      \n",
       "        <td>D7</td>\n",
       "      \n",
       "    </tr>\n",
       "  \n",
       "    <tr>\n",
       "      <td>8</td>\n",
       "      \n",
       "        <td>A8</td>\n",
       "      \n",
       "        <td>B8</td>\n",
       "      \n",
       "        <td>C8</td>\n",
       "      \n",
       "        <td>D8</td>\n",
       "      \n",
       "    </tr>\n",
       "  \n",
       "    <tr>\n",
       "      <td>9</td>\n",
       "      \n",
       "        <td>A9</td>\n",
       "      \n",
       "        <td>B9</td>\n",
       "      \n",
       "        <td>C9</td>\n",
       "      \n",
       "        <td>D9</td>\n",
       "      \n",
       "    </tr>\n",
       "  \n",
       "    <tr>\n",
       "      <td>10</td>\n",
       "      \n",
       "        <td>A10</td>\n",
       "      \n",
       "        <td>B10</td>\n",
       "      \n",
       "        <td>C10</td>\n",
       "      \n",
       "        <td>D10</td>\n",
       "      \n",
       "    </tr>\n",
       "  \n",
       "    <tr>\n",
       "      <td>11</td>\n",
       "      \n",
       "        <td>A11</td>\n",
       "      \n",
       "        <td>B11</td>\n",
       "      \n",
       "        <td>C11</td>\n",
       "      \n",
       "        <td>D11</td>\n",
       "      \n",
       "    </tr>\n",
       "  \n",
       "\n",
       "  \n",
       "</table>"
      ],
      "text/plain": [
       "#<Daru::DataFrame(12x4)>\n",
       "       A   B   C   D\n",
       "   0  A0  B0  C0  D0\n",
       "   1  A1  B1  C1  D1\n",
       "   2  A2  B2  C2  D2\n",
       "   3  A3  B3  C3  D3\n",
       "   4  A4  B4  C4  D4\n",
       "   5  A5  B5  C5  D5\n",
       "   6  A6  B6  C6  D6\n",
       "   7  A7  B7  C7  D7\n",
       "   8  A8  B8  C8  D8\n",
       "   9  A9  B9  C9  D9\n",
       "  10 A10 B10 C10 D10\n",
       "  11 A11 B11 C11 D11"
      ]
     },
     "execution_count": 2,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "df1 = Daru::DataFrame.new(\n",
    "  {\n",
    "    A:['A0', 'A1', 'A2', 'A3'],\n",
    "    B:['B0', 'B1', 'B2', 'B3'],\n",
    "    C:['C0', 'C1', 'C2', 'C3'],\n",
    "    D:['D0', 'D1', 'D2', 'D3']\n",
    "  }\n",
    ")\n",
    "\n",
    "df2 = Daru::DataFrame.new(\n",
    "  {\n",
    "    A:['A4', 'A5', 'A6', 'A7'],\n",
    "    B:['B4', 'B5', 'B6', 'B7'],\n",
    "    C:['C4', 'C5', 'C6', 'C7'],\n",
    "    D:['D4', 'D5', 'D6', 'D7']\n",
    "  }\n",
    ")\n",
    "\n",
    "df3 = Daru::DataFrame.new(\n",
    "  {\n",
    "    A:['A8', 'A9', 'A10', 'A11'],\n",
    "    B:['B8', 'B9', 'B10', 'B11'],\n",
    "    C:['C8', 'C9', 'C10', 'C11'],\n",
    "    D:['D8', 'D9', 'D10', 'D11']\n",
    "  }\n",
    ")\n",
    "df1.concat(df2).concat(df3)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 3,
   "metadata": {
    "collapsed": false
   },
   "outputs": [],
   "source": [
    "# can't generate new multi-index\n",
    "# pd.concate([df1, df2], keys=['X', 'Y'])"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 4,
   "metadata": {
    "collapsed": true
   },
   "outputs": [],
   "source": [
    "# concatenation doesn't keep multi-index\n",
    "# index become [0,1,2,3...]"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "### Set logic on the other axes"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 5,
   "metadata": {
    "collapsed": false
   },
   "outputs": [
    {
     "data": {
      "text/html": [
       "<table>\n",
       "  <tr>\n",
       "    <th colspan='4'>Daru::DataFrame(4x3)</th>\n",
       "  </tr>\n",
       "\n",
       "  \n",
       "    <tr>\n",
       "      <th></th>\n",
       "      \n",
       "        <th>B</th>\n",
       "      \n",
       "        <th>D</th>\n",
       "      \n",
       "        <th>F</th>\n",
       "      \n",
       "    </tr>\n",
       "  \n",
       "\n",
       "  \n",
       "    <tr>\n",
       "      <td>2</td>\n",
       "      \n",
       "        <td>B2</td>\n",
       "      \n",
       "        <td>D2</td>\n",
       "      \n",
       "        <td>F2</td>\n",
       "      \n",
       "    </tr>\n",
       "  \n",
       "    <tr>\n",
       "      <td>3</td>\n",
       "      \n",
       "        <td>B3</td>\n",
       "      \n",
       "        <td>D3</td>\n",
       "      \n",
       "        <td>F3</td>\n",
       "      \n",
       "    </tr>\n",
       "  \n",
       "    <tr>\n",
       "      <td>6</td>\n",
       "      \n",
       "        <td>B6</td>\n",
       "      \n",
       "        <td>D6</td>\n",
       "      \n",
       "        <td>F6</td>\n",
       "      \n",
       "    </tr>\n",
       "  \n",
       "    <tr>\n",
       "      <td>7</td>\n",
       "      \n",
       "        <td>B7</td>\n",
       "      \n",
       "        <td>D7</td>\n",
       "      \n",
       "        <td>F7</td>\n",
       "      \n",
       "    </tr>\n",
       "  \n",
       "\n",
       "  \n",
       "</table>"
      ],
      "text/plain": [
       "#<Daru::DataFrame(4x3)>\n",
       "       B   D   F\n",
       "   2  B2  D2  F2\n",
       "   3  B3  D3  F3\n",
       "   6  B6  D6  F6\n",
       "   7  B7  D7  F7"
      ]
     },
     "execution_count": 5,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "df4 = Daru::DataFrame.new(\n",
    "  {\n",
    "    B: ['B2', 'B3', 'B6', 'B7'],\n",
    "    D: ['D2', 'D3', 'D6', 'D7'],\n",
    "    F: ['F2', 'F3', 'F6', 'F7']\n",
    "  },\n",
    "  index: [2, 3, 6, 7]\n",
    ")"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "#### outer join"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 6,
   "metadata": {
    "collapsed": false
   },
   "outputs": [
    {
     "data": {
      "text/html": [
       "<table>\n",
       "  <tr>\n",
       "    <th colspan='6'>Daru::DataFrame(6x5)</th>\n",
       "  </tr>\n",
       "\n",
       "  \n",
       "    <tr>\n",
       "      <th></th>\n",
       "      \n",
       "        <th>A</th>\n",
       "      \n",
       "        <th>C</th>\n",
       "      \n",
       "        <th>B</th>\n",
       "      \n",
       "        <th>D</th>\n",
       "      \n",
       "        <th>F</th>\n",
       "      \n",
       "    </tr>\n",
       "  \n",
       "\n",
       "  \n",
       "    <tr>\n",
       "      <td>0</td>\n",
       "      \n",
       "        <td>A0</td>\n",
       "      \n",
       "        <td>C0</td>\n",
       "      \n",
       "        <td>B0</td>\n",
       "      \n",
       "        <td>D0</td>\n",
       "      \n",
       "        <td></td>\n",
       "      \n",
       "    </tr>\n",
       "  \n",
       "    <tr>\n",
       "      <td>1</td>\n",
       "      \n",
       "        <td>A1</td>\n",
       "      \n",
       "        <td>C1</td>\n",
       "      \n",
       "        <td>B1</td>\n",
       "      \n",
       "        <td>D1</td>\n",
       "      \n",
       "        <td></td>\n",
       "      \n",
       "    </tr>\n",
       "  \n",
       "    <tr>\n",
       "      <td>2</td>\n",
       "      \n",
       "        <td>A2</td>\n",
       "      \n",
       "        <td>C2</td>\n",
       "      \n",
       "        <td>B2</td>\n",
       "      \n",
       "        <td>D2</td>\n",
       "      \n",
       "        <td>F2</td>\n",
       "      \n",
       "    </tr>\n",
       "  \n",
       "    <tr>\n",
       "      <td>3</td>\n",
       "      \n",
       "        <td>A3</td>\n",
       "      \n",
       "        <td>C3</td>\n",
       "      \n",
       "        <td>B3</td>\n",
       "      \n",
       "        <td>D3</td>\n",
       "      \n",
       "        <td>F3</td>\n",
       "      \n",
       "    </tr>\n",
       "  \n",
       "    <tr>\n",
       "      <td>4</td>\n",
       "      \n",
       "        <td></td>\n",
       "      \n",
       "        <td></td>\n",
       "      \n",
       "        <td>B6</td>\n",
       "      \n",
       "        <td>D6</td>\n",
       "      \n",
       "        <td>F6</td>\n",
       "      \n",
       "    </tr>\n",
       "  \n",
       "    <tr>\n",
       "      <td>5</td>\n",
       "      \n",
       "        <td></td>\n",
       "      \n",
       "        <td></td>\n",
       "      \n",
       "        <td>B7</td>\n",
       "      \n",
       "        <td>D7</td>\n",
       "      \n",
       "        <td>F7</td>\n",
       "      \n",
       "    </tr>\n",
       "  \n",
       "\n",
       "  \n",
       "</table>"
      ],
      "text/plain": [
       "#<Daru::DataFrame(6x5)>\n",
       "       A   C   B   D   F\n",
       "   0  A0  C0  B0  D0 nil\n",
       "   1  A1  C1  B1  D1 nil\n",
       "   2  A2  C2  B2  D2  F2\n",
       "   3  A3  C3  B3  D3  F3\n",
       "   4 nil nil  B6  D6  F6\n",
       "   5 nil nil  B7  D7  F7"
      ]
     },
     "execution_count": 6,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "df1.join(df4, on: [:B, :D], how: :outer)"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "#### inner join"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 7,
   "metadata": {
    "collapsed": false
   },
   "outputs": [
    {
     "data": {
      "text/html": [
       "<table>\n",
       "  <tr>\n",
       "    <th colspan='6'>Daru::DataFrame(2x5)</th>\n",
       "  </tr>\n",
       "\n",
       "  \n",
       "    <tr>\n",
       "      <th></th>\n",
       "      \n",
       "        <th>A</th>\n",
       "      \n",
       "        <th>C</th>\n",
       "      \n",
       "        <th>B</th>\n",
       "      \n",
       "        <th>D</th>\n",
       "      \n",
       "        <th>F</th>\n",
       "      \n",
       "    </tr>\n",
       "  \n",
       "\n",
       "  \n",
       "    <tr>\n",
       "      <td>0</td>\n",
       "      \n",
       "        <td>A2</td>\n",
       "      \n",
       "        <td>C2</td>\n",
       "      \n",
       "        <td>B2</td>\n",
       "      \n",
       "        <td>D2</td>\n",
       "      \n",
       "        <td>F2</td>\n",
       "      \n",
       "    </tr>\n",
       "  \n",
       "    <tr>\n",
       "      <td>1</td>\n",
       "      \n",
       "        <td>A3</td>\n",
       "      \n",
       "        <td>C3</td>\n",
       "      \n",
       "        <td>B3</td>\n",
       "      \n",
       "        <td>D3</td>\n",
       "      \n",
       "        <td>F3</td>\n",
       "      \n",
       "    </tr>\n",
       "  \n",
       "\n",
       "  \n",
       "</table>"
      ],
      "text/plain": [
       "#<Daru::DataFrame(2x5)>\n",
       "       A   C   B   D   F\n",
       "   0  A2  C2  B2  D2  F2\n",
       "   1  A3  C3  B3  D3  F3"
      ]
     },
     "execution_count": 7,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "df1.join(df4, on: [:B, :D], how: :inner)"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "### Concatenating using append"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 8,
   "metadata": {
    "collapsed": false
   },
   "outputs": [
    {
     "data": {
      "text/html": [
       "<table>\n",
       "  <tr>\n",
       "    <th colspan='5'>Daru::DataFrame(12x4)</th>\n",
       "  </tr>\n",
       "\n",
       "  \n",
       "    <tr>\n",
       "      <th></th>\n",
       "      \n",
       "        <th>A</th>\n",
       "      \n",
       "        <th>B</th>\n",
       "      \n",
       "        <th>C</th>\n",
       "      \n",
       "        <th>D</th>\n",
       "      \n",
       "    </tr>\n",
       "  \n",
       "\n",
       "  \n",
       "    <tr>\n",
       "      <td>0</td>\n",
       "      \n",
       "        <td>A0</td>\n",
       "      \n",
       "        <td>B0</td>\n",
       "      \n",
       "        <td>C0</td>\n",
       "      \n",
       "        <td>D0</td>\n",
       "      \n",
       "    </tr>\n",
       "  \n",
       "    <tr>\n",
       "      <td>1</td>\n",
       "      \n",
       "        <td>A1</td>\n",
       "      \n",
       "        <td>B1</td>\n",
       "      \n",
       "        <td>C1</td>\n",
       "      \n",
       "        <td>D1</td>\n",
       "      \n",
       "    </tr>\n",
       "  \n",
       "    <tr>\n",
       "      <td>2</td>\n",
       "      \n",
       "        <td>A2</td>\n",
       "      \n",
       "        <td>B2</td>\n",
       "      \n",
       "        <td>C2</td>\n",
       "      \n",
       "        <td>D2</td>\n",
       "      \n",
       "    </tr>\n",
       "  \n",
       "    <tr>\n",
       "      <td>3</td>\n",
       "      \n",
       "        <td>A3</td>\n",
       "      \n",
       "        <td>B3</td>\n",
       "      \n",
       "        <td>C3</td>\n",
       "      \n",
       "        <td>D3</td>\n",
       "      \n",
       "    </tr>\n",
       "  \n",
       "    <tr>\n",
       "      <td>4</td>\n",
       "      \n",
       "        <td>A4</td>\n",
       "      \n",
       "        <td>B4</td>\n",
       "      \n",
       "        <td>C4</td>\n",
       "      \n",
       "        <td>D4</td>\n",
       "      \n",
       "    </tr>\n",
       "  \n",
       "    <tr>\n",
       "      <td>5</td>\n",
       "      \n",
       "        <td>A5</td>\n",
       "      \n",
       "        <td>B5</td>\n",
       "      \n",
       "        <td>C5</td>\n",
       "      \n",
       "        <td>D5</td>\n",
       "      \n",
       "    </tr>\n",
       "  \n",
       "    <tr>\n",
       "      <td>6</td>\n",
       "      \n",
       "        <td>A6</td>\n",
       "      \n",
       "        <td>B6</td>\n",
       "      \n",
       "        <td>C6</td>\n",
       "      \n",
       "        <td>D6</td>\n",
       "      \n",
       "    </tr>\n",
       "  \n",
       "    <tr>\n",
       "      <td>7</td>\n",
       "      \n",
       "        <td>A7</td>\n",
       "      \n",
       "        <td>B7</td>\n",
       "      \n",
       "        <td>C7</td>\n",
       "      \n",
       "        <td>D7</td>\n",
       "      \n",
       "    </tr>\n",
       "  \n",
       "    <tr>\n",
       "      <td>8</td>\n",
       "      \n",
       "        <td>A8</td>\n",
       "      \n",
       "        <td>B8</td>\n",
       "      \n",
       "        <td>C8</td>\n",
       "      \n",
       "        <td>D8</td>\n",
       "      \n",
       "    </tr>\n",
       "  \n",
       "    <tr>\n",
       "      <td>9</td>\n",
       "      \n",
       "        <td>A9</td>\n",
       "      \n",
       "        <td>B9</td>\n",
       "      \n",
       "        <td>C9</td>\n",
       "      \n",
       "        <td>D9</td>\n",
       "      \n",
       "    </tr>\n",
       "  \n",
       "    <tr>\n",
       "      <td>10</td>\n",
       "      \n",
       "        <td>A10</td>\n",
       "      \n",
       "        <td>B10</td>\n",
       "      \n",
       "        <td>C10</td>\n",
       "      \n",
       "        <td>D10</td>\n",
       "      \n",
       "    </tr>\n",
       "  \n",
       "    <tr>\n",
       "      <td>11</td>\n",
       "      \n",
       "        <td>A11</td>\n",
       "      \n",
       "        <td>B11</td>\n",
       "      \n",
       "        <td>C11</td>\n",
       "      \n",
       "        <td>D11</td>\n",
       "      \n",
       "    </tr>\n",
       "  \n",
       "\n",
       "  \n",
       "</table>"
      ],
      "text/plain": [
       "#<Daru::DataFrame(12x4)>\n",
       "       A   B   C   D\n",
       "   0  A0  B0  C0  D0\n",
       "   1  A1  B1  C1  D1\n",
       "   2  A2  B2  C2  D2\n",
       "   3  A3  B3  C3  D3\n",
       "   4  A4  B4  C4  D4\n",
       "   5  A5  B5  C5  D5\n",
       "   6  A6  B6  C6  D6\n",
       "   7  A7  B7  C7  D7\n",
       "   8  A8  B8  C8  D8\n",
       "   9  A9  B9  C9  D9\n",
       "  10 A10 B10 C10 D10\n",
       "  11 A11 B11 C11 D11"
      ]
     },
     "execution_count": 8,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "df1.concat(df2).concat(df3)"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "### Ignoring indexes on the concatenatin axis"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "Ignoring indexes is default behavior of `DataFrame#concat` method."
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "### Concatenating with mixed ndims"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "You can concatenate DataFrames with Vectors through `Vector#to_df` method."
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 9,
   "metadata": {
    "collapsed": false
   },
   "outputs": [
    {
     "data": {
      "text/html": [
       "<table>\n",
       "  <tr>\n",
       "    <th colspan='6'>Daru::DataFrame(4x5)</th>\n",
       "  </tr>\n",
       "\n",
       "  \n",
       "    <tr>\n",
       "      <th></th>\n",
       "      \n",
       "        <th>A</th>\n",
       "      \n",
       "        <th>B</th>\n",
       "      \n",
       "        <th>C</th>\n",
       "      \n",
       "        <th>D</th>\n",
       "      \n",
       "        <th>X</th>\n",
       "      \n",
       "    </tr>\n",
       "  \n",
       "\n",
       "  \n",
       "    <tr>\n",
       "      <td>0</td>\n",
       "      \n",
       "        <td>A0</td>\n",
       "      \n",
       "        <td>B0</td>\n",
       "      \n",
       "        <td>C0</td>\n",
       "      \n",
       "        <td>D0</td>\n",
       "      \n",
       "        <td>V1</td>\n",
       "      \n",
       "    </tr>\n",
       "  \n",
       "    <tr>\n",
       "      <td>1</td>\n",
       "      \n",
       "        <td>A1</td>\n",
       "      \n",
       "        <td>B1</td>\n",
       "      \n",
       "        <td>C1</td>\n",
       "      \n",
       "        <td>D1</td>\n",
       "      \n",
       "        <td>V2</td>\n",
       "      \n",
       "    </tr>\n",
       "  \n",
       "    <tr>\n",
       "      <td>2</td>\n",
       "      \n",
       "        <td>A2</td>\n",
       "      \n",
       "        <td>B2</td>\n",
       "      \n",
       "        <td>C2</td>\n",
       "      \n",
       "        <td>D2</td>\n",
       "      \n",
       "        <td>V3</td>\n",
       "      \n",
       "    </tr>\n",
       "  \n",
       "    <tr>\n",
       "      <td>3</td>\n",
       "      \n",
       "        <td>A3</td>\n",
       "      \n",
       "        <td>B3</td>\n",
       "      \n",
       "        <td>C3</td>\n",
       "      \n",
       "        <td>D3</td>\n",
       "      \n",
       "        <td>V4</td>\n",
       "      \n",
       "    </tr>\n",
       "  \n",
       "\n",
       "  \n",
       "</table>"
      ],
      "text/plain": [
       "#<Daru::DataFrame(4x5)>\n",
       "       A   B   C   D   X\n",
       "   0  A0  B0  C0  D0  V1\n",
       "   1  A1  B1  C1  D1  V2\n",
       "   2  A2  B2  C2  D2  V3\n",
       "   3  A3  B3  C3  D3  V4"
      ]
     },
     "execution_count": 9,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "v1 = Daru::Vector.new(['V1', 'V2', 'V3', 'V4'], name: :X)\n",
    "Daru::DataFrame.new(df1.to_hash.merge(v1.to_df.to_hash))"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "### More concatenating with group keys"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 10,
   "metadata": {
    "collapsed": false
   },
   "outputs": [
    {
     "data": {
      "text/html": [
       "<table>\n",
       "  <tr>\n",
       "    <th colspan='3'>Daru::DataFrame(4x2)</th>\n",
       "  </tr>\n",
       "\n",
       "  \n",
       "    <tr>\n",
       "      <th></th>\n",
       "      \n",
       "        <th></th>\n",
       "      \n",
       "        <th>foo</th>\n",
       "      \n",
       "    </tr>\n",
       "  \n",
       "\n",
       "  \n",
       "    <tr>\n",
       "      <td>0</td>\n",
       "      \n",
       "        <td>e</td>\n",
       "      \n",
       "        <td>a</td>\n",
       "      \n",
       "    </tr>\n",
       "  \n",
       "    <tr>\n",
       "      <td>1</td>\n",
       "      \n",
       "        <td>f</td>\n",
       "      \n",
       "        <td>v</td>\n",
       "      \n",
       "    </tr>\n",
       "  \n",
       "    <tr>\n",
       "      <td>2</td>\n",
       "      \n",
       "        <td>g</td>\n",
       "      \n",
       "        <td>c</td>\n",
       "      \n",
       "    </tr>\n",
       "  \n",
       "    <tr>\n",
       "      <td>3</td>\n",
       "      \n",
       "        <td>h</td>\n",
       "      \n",
       "        <td>d</td>\n",
       "      \n",
       "    </tr>\n",
       "  \n",
       "\n",
       "  \n",
       "</table>"
      ],
      "text/plain": [
       "#<Daru::DataFrame(4x2)>\n",
       "         foo\n",
       "   0   e   a\n",
       "   1   f   v\n",
       "   2   g   c\n",
       "   3   h   d"
      ]
     },
     "execution_count": 10,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "v2 = Daru::Vector.new([:a, :v, :c, :d], name:'foo')\n",
    "v3 = Daru::Vector.new([:x, :y, :z, :z])\n",
    "v4 = Daru::Vector.new([:e, :f, :g, :h])\n",
    "# when concatenate several dataframes without name like below, the last one is kept and others disappear\n",
    "df5 = Daru::DataFrame.new(v2.to_df.to_hash.merge(v3.to_df.to_hash).merge(v4.to_df.to_hash))"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "### Appending rows to a DataFrame"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 11,
   "metadata": {
    "collapsed": false
   },
   "outputs": [
    {
     "data": {
      "text/html": [
       "<table>\n",
       "  <tr>\n",
       "    <th colspan='5'>Daru::DataFrame(5x4)</th>\n",
       "  </tr>\n",
       "\n",
       "  \n",
       "    <tr>\n",
       "      <th></th>\n",
       "      \n",
       "        <th>A</th>\n",
       "      \n",
       "        <th>B</th>\n",
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       "        <th>C</th>\n",
       "      \n",
       "        <th>D</th>\n",
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       "  \n",
       "\n",
       "  \n",
       "    <tr>\n",
       "      <td>0</td>\n",
       "      \n",
       "        <td>A0</td>\n",
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       "        <td>C0</td>\n",
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       "        <td>D0</td>\n",
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       "      <td>1</td>\n",
       "      \n",
       "        <td>A1</td>\n",
       "      \n",
       "        <td>B1</td>\n",
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       "        <td>C1</td>\n",
       "      \n",
       "        <td>D1</td>\n",
       "      \n",
       "    </tr>\n",
       "  \n",
       "    <tr>\n",
       "      <td>2</td>\n",
       "      \n",
       "        <td>A2</td>\n",
       "      \n",
       "        <td>B2</td>\n",
       "      \n",
       "        <td>C2</td>\n",
       "      \n",
       "        <td>D2</td>\n",
       "      \n",
       "    </tr>\n",
       "  \n",
       "    <tr>\n",
       "      <td>3</td>\n",
       "      \n",
       "        <td>A3</td>\n",
       "      \n",
       "        <td>B3</td>\n",
       "      \n",
       "        <td>C3</td>\n",
       "      \n",
       "        <td>D3</td>\n",
       "      \n",
       "    </tr>\n",
       "  \n",
       "    <tr>\n",
       "      <td>4</td>\n",
       "      \n",
       "        <td>X0</td>\n",
       "      \n",
       "        <td>X1</td>\n",
       "      \n",
       "        <td>X2</td>\n",
       "      \n",
       "        <td>X3</td>\n",
       "      \n",
       "    </tr>\n",
       "  \n",
       "\n",
       "  \n",
       "</table>"
      ],
      "text/plain": [
       "#<Daru::DataFrame(5x4)>\n",
       "       A   B   C   D\n",
       "   0  A0  B0  C0  D0\n",
       "   1  A1  B1  C1  D1\n",
       "   2  A2  B2  C2  D2\n",
       "   3  A3  B3  C3  D3\n",
       "   4  X0  X1  X2  X3"
      ]
     },
     "execution_count": 11,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "df1.concat(\n",
    "  Daru::DataFrame.rows([['X0', 'X1', 'X2', 'X3']], order: [:A, :B, :C, :D])\n",
    ")"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 12,
   "metadata": {
    "collapsed": false
   },
   "outputs": [
    {
     "data": {
      "text/html": [
       "<table>\n",
       "  <tr>\n",
       "    <th colspan='5'>Daru::DataFrame(5x4)</th>\n",
       "  </tr>\n",
       "\n",
       "  \n",
       "    <tr>\n",
       "      <th></th>\n",
       "      \n",
       "        <th>A</th>\n",
       "      \n",
       "        <th>B</th>\n",
       "      \n",
       "        <th>C</th>\n",
       "      \n",
       "        <th>D</th>\n",
       "      \n",
       "    </tr>\n",
       "  \n",
       "\n",
       "  \n",
       "    <tr>\n",
       "      <td>0</td>\n",
       "      \n",
       "        <td>A0</td>\n",
       "      \n",
       "        <td>B0</td>\n",
       "      \n",
       "        <td>C0</td>\n",
       "      \n",
       "        <td>D0</td>\n",
       "      \n",
       "    </tr>\n",
       "  \n",
       "    <tr>\n",
       "      <td>1</td>\n",
       "      \n",
       "        <td>A1</td>\n",
       "      \n",
       "        <td>B1</td>\n",
       "      \n",
       "        <td>C1</td>\n",
       "      \n",
       "        <td>D1</td>\n",
       "      \n",
       "    </tr>\n",
       "  \n",
       "    <tr>\n",
       "      <td>2</td>\n",
       "      \n",
       "        <td>A2</td>\n",
       "      \n",
       "        <td>B2</td>\n",
       "      \n",
       "        <td>C2</td>\n",
       "      \n",
       "        <td>D2</td>\n",
       "      \n",
       "    </tr>\n",
       "  \n",
       "    <tr>\n",
       "      <td>3</td>\n",
       "      \n",
       "        <td>A3</td>\n",
       "      \n",
       "        <td>B3</td>\n",
       "      \n",
       "        <td>C3</td>\n",
       "      \n",
       "        <td>D3</td>\n",
       "      \n",
       "    </tr>\n",
       "  \n",
       "    <tr>\n",
       "      <td>4</td>\n",
       "      \n",
       "        <td>X0</td>\n",
       "      \n",
       "        <td>X1</td>\n",
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       "        <td>X2</td>\n",
       "      \n",
       "        <td>X3</td>\n",
       "      \n",
       "    </tr>\n",
       "  \n",
       "\n",
       "  \n",
       "</table>"
      ],
      "text/plain": [
       "#<Daru::DataFrame(5x4)>\n",
       "       A   B   C   D\n",
       "   0  A0  B0  C0  D0\n",
       "   1  A1  B1  C1  D1\n",
       "   2  A2  B2  C2  D2\n",
       "   3  A3  B3  C3  D3\n",
       "   4  X0  X1  X2  X3"
      ]
     },
     "execution_count": 12,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "_df1 = df1.dup\n",
    "# \"add_row\" method makes side-effect, not returning new DataFrame\n",
    "_df1.add_row(['X0', 'X1', 'X2', 'X3'])\n",
    "_df1"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 13,
   "metadata": {
    "collapsed": false
   },
   "outputs": [
    {
     "data": {
      "text/html": [
       "<table>\n",
       "  <tr>\n",
       "    <th colspan='6'>Daru::DataFrame(5x5)</th>\n",
       "  </tr>\n",
       "\n",
       "  \n",
       "    <tr>\n",
       "      <th></th>\n",
       "      \n",
       "        <th>A</th>\n",
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       "        <th>B</th>\n",
       "      \n",
       "        <th>C</th>\n",
       "      \n",
       "        <th>D</th>\n",
       "      \n",
       "        <th>X</th>\n",
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       "  \n",
       "\n",
       "  \n",
       "    <tr>\n",
       "      <td>0</td>\n",
       "      \n",
       "        <td>A0</td>\n",
       "      \n",
       "        <td>B0</td>\n",
       "      \n",
       "        <td>C0</td>\n",
       "      \n",
       "        <td>D0</td>\n",
       "      \n",
       "        <td></td>\n",
       "      \n",
       "    </tr>\n",
       "  \n",
       "    <tr>\n",
       "      <td>1</td>\n",
       "      \n",
       "        <td>A1</td>\n",
       "      \n",
       "        <td>B1</td>\n",
       "      \n",
       "        <td>C1</td>\n",
       "      \n",
       "        <td>D1</td>\n",
       "      \n",
       "        <td></td>\n",
       "      \n",
       "    </tr>\n",
       "  \n",
       "    <tr>\n",
       "      <td>2</td>\n",
       "      \n",
       "        <td>A2</td>\n",
       "      \n",
       "        <td>B2</td>\n",
       "      \n",
       "        <td>C2</td>\n",
       "      \n",
       "        <td>D2</td>\n",
       "      \n",
       "        <td></td>\n",
       "      \n",
       "    </tr>\n",
       "  \n",
       "    <tr>\n",
       "      <td>3</td>\n",
       "      \n",
       "        <td>A3</td>\n",
       "      \n",
       "        <td>B3</td>\n",
       "      \n",
       "        <td>C3</td>\n",
       "      \n",
       "        <td>D3</td>\n",
       "      \n",
       "        <td></td>\n",
       "      \n",
       "    </tr>\n",
       "  \n",
       "    <tr>\n",
       "      <td>4</td>\n",
       "      \n",
       "        <td>X0</td>\n",
       "      \n",
       "        <td>X1</td>\n",
       "      \n",
       "        <td>X2</td>\n",
       "      \n",
       "        <td></td>\n",
       "      \n",
       "        <td>X3</td>\n",
       "      \n",
       "    </tr>\n",
       "  \n",
       "\n",
       "  \n",
       "</table>"
      ],
      "text/plain": [
       "#<Daru::DataFrame(5x5)>\n",
       "       A   B   C   D   X\n",
       "   0  A0  B0  C0  D0 nil\n",
       "   1  A1  B1  C1  D1 nil\n",
       "   2  A2  B2  C2  D2 nil\n",
       "   3  A3  B3  C3  D3 nil\n",
       "   4  X0  X1  X2 nil  X3"
      ]
     },
     "execution_count": 13,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "df1.concat(\n",
    "  Daru::DataFrame.rows([['X0', 'X1', 'X2', 'X3']], order: [:A, :B, :C, :X])\n",
    ")"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## Database-style DataFrame joining/merging"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "### Brief primer on merge methods (relational algebra)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 14,
   "metadata": {
    "collapsed": false
   },
   "outputs": [
    {
     "data": {
      "text/html": [
       "<table>\n",
       "  <tr>\n",
       "    <th colspan='6'>Daru::DataFrame(4x5)</th>\n",
       "  </tr>\n",
       "\n",
       "  \n",
       "    <tr>\n",
       "      <th></th>\n",
       "      \n",
       "        <th>A</th>\n",
       "      \n",
       "        <th>B</th>\n",
       "      \n",
       "        <th>key</th>\n",
       "      \n",
       "        <th>C</th>\n",
       "      \n",
       "        <th>D</th>\n",
       "      \n",
       "    </tr>\n",
       "  \n",
       "\n",
       "  \n",
       "    <tr>\n",
       "      <td>0</td>\n",
       "      \n",
       "        <td>A0</td>\n",
       "      \n",
       "        <td>B0</td>\n",
       "      \n",
       "        <td>K0</td>\n",
       "      \n",
       "        <td>C0</td>\n",
       "      \n",
       "        <td>D0</td>\n",
       "      \n",
       "    </tr>\n",
       "  \n",
       "    <tr>\n",
       "      <td>1</td>\n",
       "      \n",
       "        <td>A1</td>\n",
       "      \n",
       "        <td>B1</td>\n",
       "      \n",
       "        <td>K1</td>\n",
       "      \n",
       "        <td>C1</td>\n",
       "      \n",
       "        <td>D1</td>\n",
       "      \n",
       "    </tr>\n",
       "  \n",
       "    <tr>\n",
       "      <td>2</td>\n",
       "      \n",
       "        <td>A2</td>\n",
       "      \n",
       "        <td>B2</td>\n",
       "      \n",
       "        <td>K2</td>\n",
       "      \n",
       "        <td>C2</td>\n",
       "      \n",
       "        <td>D2</td>\n",
       "      \n",
       "    </tr>\n",
       "  \n",
       "    <tr>\n",
       "      <td>3</td>\n",
       "      \n",
       "        <td>A3</td>\n",
       "      \n",
       "        <td>B3</td>\n",
       "      \n",
       "        <td>K3</td>\n",
       "      \n",
       "        <td>C3</td>\n",
       "      \n",
       "        <td>D3</td>\n",
       "      \n",
       "    </tr>\n",
       "  \n",
       "\n",
       "  \n",
       "</table>"
      ],
      "text/plain": [
       "#<Daru::DataFrame(4x5)>\n",
       "       A   B key   C   D\n",
       "   0  A0  B0  K0  C0  D0\n",
       "   1  A1  B1  K1  C1  D1\n",
       "   2  A2  B2  K2  C2  D2\n",
       "   3  A3  B3  K3  C3  D3"
      ]
     },
     "execution_count": 14,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "left = Daru::DataFrame.new(\n",
    "  key: ['K0', 'K1', 'K2', 'K3'],\n",
    "  A: ['A0', 'A1', 'A2', 'A3'],\n",
    "  B: ['B0', 'B1', 'B2', 'B3']\n",
    ")\n",
    "\n",
    "right = Daru::DataFrame.new(\n",
    "  key: ['K0', 'K1', 'K2', 'K3'],\n",
    "  C: ['C0', 'C1', 'C2', 'C3'],\n",
    "  D: ['D0', 'D1', 'D2', 'D3']\n",
    ")\n",
    "\n",
    "left.join(right, on:[:key], how: :inner)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 15,
   "metadata": {
    "collapsed": false
   },
   "outputs": [
    {
     "data": {
      "text/html": [
       "<table>\n",
       "  <tr>\n",
       "    <th colspan='7'>Daru::DataFrame(3x6)</th>\n",
       "  </tr>\n",
       "\n",
       "  \n",
       "    <tr>\n",
       "      <th></th>\n",
       "      \n",
       "        <th>A</th>\n",
       "      \n",
       "        <th>B</th>\n",
       "      \n",
       "        <th>key1</th>\n",
       "      \n",
       "        <th>key2</th>\n",
       "      \n",
       "        <th>C</th>\n",
       "      \n",
       "        <th>D</th>\n",
       "      \n",
       "    </tr>\n",
       "  \n",
       "\n",
       "  \n",
       "    <tr>\n",
       "      <td>0</td>\n",
       "      \n",
       "        <td>A0</td>\n",
       "      \n",
       "        <td>B0</td>\n",
       "      \n",
       "        <td>K0</td>\n",
       "      \n",
       "        <td>K0</td>\n",
       "      \n",
       "        <td>C0</td>\n",
       "      \n",
       "        <td>D0</td>\n",
       "      \n",
       "    </tr>\n",
       "  \n",
       "    <tr>\n",
       "      <td>1</td>\n",
       "      \n",
       "        <td>A2</td>\n",
       "      \n",
       "        <td>B2</td>\n",
       "      \n",
       "        <td>K1</td>\n",
       "      \n",
       "        <td>K0</td>\n",
       "      \n",
       "        <td>C1</td>\n",
       "      \n",
       "        <td>D1</td>\n",
       "      \n",
       "    </tr>\n",
       "  \n",
       "    <tr>\n",
       "      <td>2</td>\n",
       "      \n",
       "        <td>A2</td>\n",
       "      \n",
       "        <td>B2</td>\n",
       "      \n",
       "        <td>K1</td>\n",
       "      \n",
       "        <td>K0</td>\n",
       "      \n",
       "        <td>C2</td>\n",
       "      \n",
       "        <td>D2</td>\n",
       "      \n",
       "    </tr>\n",
       "  \n",
       "\n",
       "  \n",
       "</table>"
      ],
      "text/plain": [
       "#<Daru::DataFrame(3x6)>\n",
       "         A    B key1 key2    C    D\n",
       "    0   A0   B0   K0   K0   C0   D0\n",
       "    1   A2   B2   K1   K0   C1   D1\n",
       "    2   A2   B2   K1   K0   C2   D2"
      ]
     },
     "execution_count": 15,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "left = Daru::DataFrame.new(\n",
    "  key1: ['K0', 'K0', 'K1', 'K2'],\n",
    "  key2: ['K0', 'K1', 'K0', 'K1'],\n",
    "  A: ['A0', 'A1', 'A2', 'A3'],\n",
    "  B: ['B0', 'B1', 'B2', 'B3']\n",
    ")\n",
    "\n",
    "right = Daru::DataFrame.new(\n",
    "  key1: ['K0', 'K1', 'K1', 'K2'],\n",
    "  key2: ['K0', 'K0', 'K0', 'K0'],\n",
    "  C: ['C0', 'C1', 'C2', 'C3'],\n",
    "  D: ['D0', 'D1', 'D2', 'D3']\n",
    ")\n",
    "\n",
    "left.join(right, on:[:key1, :key2], how: :inner)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 16,
   "metadata": {
    "collapsed": false
   },
   "outputs": [
    {
     "data": {
      "text/html": [
       "<table>\n",
       "  <tr>\n",
       "    <th colspan='7'>Daru::DataFrame(5x6)</th>\n",
       "  </tr>\n",
       "\n",
       "  \n",
       "    <tr>\n",
       "      <th></th>\n",
       "      \n",
       "        <th>A</th>\n",
       "      \n",
       "        <th>B</th>\n",
       "      \n",
       "        <th>key1</th>\n",
       "      \n",
       "        <th>key2</th>\n",
       "      \n",
       "        <th>C</th>\n",
       "      \n",
       "        <th>D</th>\n",
       "      \n",
       "    </tr>\n",
       "  \n",
       "\n",
       "  \n",
       "    <tr>\n",
       "      <td>0</td>\n",
       "      \n",
       "        <td>A0</td>\n",
       "      \n",
       "        <td>B0</td>\n",
       "      \n",
       "        <td>K0</td>\n",
       "      \n",
       "        <td>K0</td>\n",
       "      \n",
       "        <td>C0</td>\n",
       "      \n",
       "        <td>D0</td>\n",
       "      \n",
       "    </tr>\n",
       "  \n",
       "    <tr>\n",
       "      <td>1</td>\n",
       "      \n",
       "        <td>A1</td>\n",
       "      \n",
       "        <td>B1</td>\n",
       "      \n",
       "        <td>K0</td>\n",
       "      \n",
       "        <td>K1</td>\n",
       "      \n",
       "        <td></td>\n",
       "      \n",
       "        <td></td>\n",
       "      \n",
       "    </tr>\n",
       "  \n",
       "    <tr>\n",
       "      <td>2</td>\n",
       "      \n",
       "        <td>A2</td>\n",
       "      \n",
       "        <td>B2</td>\n",
       "      \n",
       "        <td>K1</td>\n",
       "      \n",
       "        <td>K0</td>\n",
       "      \n",
       "        <td>C1</td>\n",
       "      \n",
       "        <td>D1</td>\n",
       "      \n",
       "    </tr>\n",
       "  \n",
       "    <tr>\n",
       "      <td>3</td>\n",
       "      \n",
       "        <td>A2</td>\n",
       "      \n",
       "        <td>B2</td>\n",
       "      \n",
       "        <td>K1</td>\n",
       "      \n",
       "        <td>K0</td>\n",
       "      \n",
       "        <td>C2</td>\n",
       "      \n",
       "        <td>D2</td>\n",
       "      \n",
       "    </tr>\n",
       "  \n",
       "    <tr>\n",
       "      <td>4</td>\n",
       "      \n",
       "        <td>A3</td>\n",
       "      \n",
       "        <td>B3</td>\n",
       "      \n",
       "        <td>K2</td>\n",
       "      \n",
       "        <td>K1</td>\n",
       "      \n",
       "        <td></td>\n",
       "      \n",
       "        <td></td>\n",
       "      \n",
       "    </tr>\n",
       "  \n",
       "\n",
       "  \n",
       "</table>"
      ],
      "text/plain": [
       "#<Daru::DataFrame(5x6)>\n",
       "         A    B key1 key2    C    D\n",
       "    0   A0   B0   K0   K0   C0   D0\n",
       "    1   A1   B1   K0   K1  nil  nil\n",
       "    2   A2   B2   K1   K0   C1   D1\n",
       "    3   A2   B2   K1   K0   C2   D2\n",
       "    4   A3   B3   K2   K1  nil  nil"
      ]
     },
     "execution_count": 16,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "left.join(right, on:[:key1, :key2], how: :left)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 17,
   "metadata": {
    "collapsed": false
   },
   "outputs": [
    {
     "data": {
      "text/html": [
       "<table>\n",
       "  <tr>\n",
       "    <th colspan='7'>Daru::DataFrame(6x6)</th>\n",
       "  </tr>\n",
       "\n",
       "  \n",
       "    <tr>\n",
       "      <th></th>\n",
       "      \n",
       "        <th>A</th>\n",
       "      \n",
       "        <th>B</th>\n",
       "      \n",
       "        <th>key1</th>\n",
       "      \n",
       "        <th>key2</th>\n",
       "      \n",
       "        <th>C</th>\n",
       "      \n",
       "        <th>D</th>\n",
       "      \n",
       "    </tr>\n",
       "  \n",
       "\n",
       "  \n",
       "    <tr>\n",
       "      <td>0</td>\n",
       "      \n",
       "        <td>A0</td>\n",
       "      \n",
       "        <td>B0</td>\n",
       "      \n",
       "        <td>K0</td>\n",
       "      \n",
       "        <td>K0</td>\n",
       "      \n",
       "        <td>C0</td>\n",
       "      \n",
       "        <td>D0</td>\n",
       "      \n",
       "    </tr>\n",
       "  \n",
       "    <tr>\n",
       "      <td>1</td>\n",
       "      \n",
       "        <td>A1</td>\n",
       "      \n",
       "        <td>B1</td>\n",
       "      \n",
       "        <td>K0</td>\n",
       "      \n",
       "        <td>K1</td>\n",
       "      \n",
       "        <td></td>\n",
       "      \n",
       "        <td></td>\n",
       "      \n",
       "    </tr>\n",
       "  \n",
       "    <tr>\n",
       "      <td>2</td>\n",
       "      \n",
       "        <td>A2</td>\n",
       "      \n",
       "        <td>B2</td>\n",
       "      \n",
       "        <td>K1</td>\n",
       "      \n",
       "        <td>K0</td>\n",
       "      \n",
       "        <td>C1</td>\n",
       "      \n",
       "        <td>D1</td>\n",
       "      \n",
       "    </tr>\n",
       "  \n",
       "    <tr>\n",
       "      <td>3</td>\n",
       "      \n",
       "        <td>A2</td>\n",
       "      \n",
       "        <td>B2</td>\n",
       "      \n",
       "        <td>K1</td>\n",
       "      \n",
       "        <td>K0</td>\n",
       "      \n",
       "        <td>C2</td>\n",
       "      \n",
       "        <td>D2</td>\n",
       "      \n",
       "    </tr>\n",
       "  \n",
       "    <tr>\n",
       "      <td>4</td>\n",
       "      \n",
       "        <td></td>\n",
       "      \n",
       "        <td></td>\n",
       "      \n",
       "        <td>K2</td>\n",
       "      \n",
       "        <td>K0</td>\n",
       "      \n",
       "        <td>C3</td>\n",
       "      \n",
       "        <td>D3</td>\n",
       "      \n",
       "    </tr>\n",
       "  \n",
       "    <tr>\n",
       "      <td>5</td>\n",
       "      \n",
       "        <td>A3</td>\n",
       "      \n",
       "        <td>B3</td>\n",
       "      \n",
       "        <td>K2</td>\n",
       "      \n",
       "        <td>K1</td>\n",
       "      \n",
       "        <td></td>\n",
       "      \n",
       "        <td></td>\n",
       "      \n",
       "    </tr>\n",
       "  \n",
       "\n",
       "  \n",
       "</table>"
      ],
      "text/plain": [
       "#<Daru::DataFrame(6x6)>\n",
       "         A    B key1 key2    C    D\n",
       "    0   A0   B0   K0   K0   C0   D0\n",
       "    1   A1   B1   K0   K1  nil  nil\n",
       "    2   A2   B2   K1   K0   C1   D1\n",
       "    3   A2   B2   K1   K0   C2   D2\n",
       "    4  nil  nil   K2   K0   C3   D3\n",
       "    5   A3   B3   K2   K1  nil  nil"
      ]
     },
     "execution_count": 17,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "left.join(right, on:[:key1, :key2], how: :outer)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 18,
   "metadata": {
    "collapsed": false
   },
   "outputs": [
    {
     "data": {
      "text/html": [
       "<table>\n",
       "  <tr>\n",
       "    <th colspan='7'>Daru::DataFrame(3x6)</th>\n",
       "  </tr>\n",
       "\n",
       "  \n",
       "    <tr>\n",
       "      <th></th>\n",
       "      \n",
       "        <th>A</th>\n",
       "      \n",
       "        <th>B</th>\n",
       "      \n",
       "        <th>key1</th>\n",
       "      \n",
       "        <th>key2</th>\n",
       "      \n",
       "        <th>C</th>\n",
       "      \n",
       "        <th>D</th>\n",
       "      \n",
       "    </tr>\n",
       "  \n",
       "\n",
       "  \n",
       "    <tr>\n",
       "      <td>0</td>\n",
       "      \n",
       "        <td>A0</td>\n",
       "      \n",
       "        <td>B0</td>\n",
       "      \n",
       "        <td>K0</td>\n",
       "      \n",
       "        <td>K0</td>\n",
       "      \n",
       "        <td>C0</td>\n",
       "      \n",
       "        <td>D0</td>\n",
       "      \n",
       "    </tr>\n",
       "  \n",
       "    <tr>\n",
       "      <td>1</td>\n",
       "      \n",
       "        <td>A2</td>\n",
       "      \n",
       "        <td>B2</td>\n",
       "      \n",
       "        <td>K1</td>\n",
       "      \n",
       "        <td>K0</td>\n",
       "      \n",
       "        <td>C1</td>\n",
       "      \n",
       "        <td>D1</td>\n",
       "      \n",
       "    </tr>\n",
       "  \n",
       "    <tr>\n",
       "      <td>2</td>\n",
       "      \n",
       "        <td>A2</td>\n",
       "      \n",
       "        <td>B2</td>\n",
       "      \n",
       "        <td>K1</td>\n",
       "      \n",
       "        <td>K0</td>\n",
       "      \n",
       "        <td>C2</td>\n",
       "      \n",
       "        <td>D2</td>\n",
       "      \n",
       "    </tr>\n",
       "  \n",
       "\n",
       "  \n",
       "</table>"
      ],
      "text/plain": [
       "#<Daru::DataFrame(3x6)>\n",
       "         A    B key1 key2    C    D\n",
       "    0   A0   B0   K0   K0   C0   D0\n",
       "    1   A2   B2   K1   K0   C1   D1\n",
       "    2   A2   B2   K1   K0   C2   D2"
      ]
     },
     "execution_count": 18,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "left.join(right, on:[:key1, :key2], how: :inner)"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "### The merge indicator"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 19,
   "metadata": {
    "collapsed": true
   },
   "outputs": [],
   "source": [
    "# there's no indicator option."
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "### Joining on index"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 20,
   "metadata": {
    "collapsed": false
   },
   "outputs": [],
   "source": [
    "# can't join on index\n",
    "\n",
    "#left = Daru::DataFrame.new({\n",
    "#  A: ['A0', 'A1', 'A2', 'A3'],\n",
    "#  B: ['B0', 'B1', 'B2', 'B3']},\n",
    "#  index: ['K0', 'K1', 'K2', 'K3']\n",
    "#)\n",
    "#\n",
    "#right = Daru::DataFrame.new({\n",
    "#  C: ['C0', 'C1', 'C2', 'C3'],\n",
    "#  D: ['D0', 'D1', 'D2', 'D3']},\n",
    "#  index: ['K0', 'K1', 'K2', 'K3'],\n",
    "#)\n",
    "#\n",
    "#left.join(right, how: :inner)"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "### Joining key columns on an index"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 21,
   "metadata": {
    "collapsed": true
   },
   "outputs": [],
   "source": [
    "## no feature\n",
    "# joining between name and index"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "### Joining a single Index to a Multi-index"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 22,
   "metadata": {
    "collapsed": true
   },
   "outputs": [],
   "source": [
    "## no feature\n",
    "## multi-index feature also doesn't exist."
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "### Joining with two multi-indexes"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 23,
   "metadata": {
    "collapsed": true
   },
   "outputs": [],
   "source": [
    "## no feature\n",
    "## multi-index feature also doesn't exist."
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "### Overlapping value columns"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 24,
   "metadata": {
    "collapsed": false
   },
   "outputs": [
    {
     "data": {
      "text/html": [
       "<table>\n",
       "  <tr>\n",
       "    <th colspan='4'>Daru::DataFrame(2x3)</th>\n",
       "  </tr>\n",
       "\n",
       "  \n",
       "    <tr>\n",
       "      <th></th>\n",
       "      \n",
       "        <th>v_1</th>\n",
       "      \n",
       "        <th>k</th>\n",
       "      \n",
       "        <th>v_2</th>\n",
       "      \n",
       "    </tr>\n",
       "  \n",
       "\n",
       "  \n",
       "    <tr>\n",
       "      <td>0</td>\n",
       "      \n",
       "        <td>1</td>\n",
       "      \n",
       "        <td>K0</td>\n",
       "      \n",
       "        <td>4</td>\n",
       "      \n",
       "    </tr>\n",
       "  \n",
       "    <tr>\n",
       "      <td>1</td>\n",
       "      \n",
       "        <td>1</td>\n",
       "      \n",
       "        <td>K0</td>\n",
       "      \n",
       "        <td>5</td>\n",
       "      \n",
       "    </tr>\n",
       "  \n",
       "\n",
       "  \n",
       "</table>"
      ],
      "text/plain": [
       "#<Daru::DataFrame(2x3)>\n",
       "     v_1   k v_2\n",
       "   0   1  K0   4\n",
       "   1   1  K0   5"
      ]
     },
     "execution_count": 24,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "left = Daru::DataFrame.new(k: ['K0', 'K1', 'K2'], v: [1, 2, 3])\n",
    "right = Daru::DataFrame.new(k: ['K0', 'K0', 'K3'], v: [4, 5, 6])\n",
    "\n",
    "left.join(right, on: [:k], how: :inner)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 25,
   "metadata": {
    "collapsed": true
   },
   "outputs": [],
   "source": [
    "## Can't specify suffixes"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "### Joining multiple DataFrame or Panel objects"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 26,
   "metadata": {
    "collapsed": true
   },
   "outputs": [],
   "source": [
    "## Can't join multiple DataFrame at once"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "### Merging Ordered Data"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 27,
   "metadata": {
    "collapsed": true
   },
   "outputs": [],
   "source": [
    "## I can't understand pandas's ordered_merge method's behavior."
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "### Merging together values within Series or DataFrame columns"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 28,
   "metadata": {
    "collapsed": true
   },
   "outputs": [],
   "source": [
    "## there's no methods like 'combine_first' or 'update'."
   ]
  }
 ],
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