how_to_use_pandas_groupby_method.ipynb

{
 "cells": [
  {
   "cell_type": "code",
   "execution_count": 9,
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/html": [
       "<div>\n",
       "<style scoped>\n",
       "    .dataframe tbody tr th:only-of-type {\n",
       "        vertical-align: middle;\n",
       "    }\n",
       "\n",
       "    .dataframe tbody tr th {\n",
       "        vertical-align: top;\n",
       "    }\n",
       "\n",
       "    .dataframe thead th {\n",
       "        text-align: right;\n",
       "    }\n",
       "</style>\n",
       "<table border=\"1\" class=\"dataframe\">\n",
       "  <thead>\n",
       "    <tr style=\"text-align: right;\">\n",
       "      <th></th>\n",
       "      <th>rank</th>\n",
       "      <th>discipline</th>\n",
       "      <th>yrs.since.phd</th>\n",
       "      <th>yrs.service</th>\n",
       "      <th>sex</th>\n",
       "      <th>salary</th>\n",
       "    </tr>\n",
       "  </thead>\n",
       "  <tbody>\n",
       "    <tr>\n",
       "      <td>1</td>\n",
       "      <td>Prof</td>\n",
       "      <td>B</td>\n",
       "      <td>19</td>\n",
       "      <td>18</td>\n",
       "      <td>Male</td>\n",
       "      <td>139750</td>\n",
       "    </tr>\n",
       "    <tr>\n",
       "      <td>2</td>\n",
       "      <td>Prof</td>\n",
       "      <td>B</td>\n",
       "      <td>20</td>\n",
       "      <td>16</td>\n",
       "      <td>Male</td>\n",
       "      <td>173200</td>\n",
       "    </tr>\n",
       "    <tr>\n",
       "      <td>3</td>\n",
       "      <td>AsstProf</td>\n",
       "      <td>B</td>\n",
       "      <td>4</td>\n",
       "      <td>3</td>\n",
       "      <td>Male</td>\n",
       "      <td>79750</td>\n",
       "    </tr>\n",
       "    <tr>\n",
       "      <td>4</td>\n",
       "      <td>Prof</td>\n",
       "      <td>B</td>\n",
       "      <td>45</td>\n",
       "      <td>39</td>\n",
       "      <td>Male</td>\n",
       "      <td>115000</td>\n",
       "    </tr>\n",
       "    <tr>\n",
       "      <td>5</td>\n",
       "      <td>Prof</td>\n",
       "      <td>B</td>\n",
       "      <td>40</td>\n",
       "      <td>41</td>\n",
       "      <td>Male</td>\n",
       "      <td>141500</td>\n",
       "    </tr>\n",
       "  </tbody>\n",
       "</table>\n",
       "</div>"
      ],
      "text/plain": [
       "       rank discipline  yrs.since.phd  yrs.service   sex  salary\n",
       "1      Prof          B             19           18  Male  139750\n",
       "2      Prof          B             20           16  Male  173200\n",
       "3  AsstProf          B              4            3  Male   79750\n",
       "4      Prof          B             45           39  Male  115000\n",
       "5      Prof          B             40           41  Male  141500"
      ]
     },
     "execution_count": 9,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "import pandas as pd\n",
    "import numpy as np\n",
    "\n",
    "data_url = 'http://vincentarelbundock.github.io/Rdatasets/csv/carData/Salaries.csv'\n",
    "df = pd.read_csv(data_url, index_col=0)\n",
    "\n",
    "df.head()"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 10,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "agg        corr      cumsum     get_group  mean     pct_change  sem    transform\n",
      "aggregate  corrwith  describe   head       median   pipe        shift  tshift   \n",
      "all        count     diff       hist       min      plot        size   var      \n",
      "any        cov       expanding  idxmax     ngroup   prod        skew \n",
      "apply      cumcount  ffill      idxmin     nth      quantile    std  \n",
      "backfill   cummax    fillna     last       nunique  rank        sum  \n",
      "bfill      cummin    filter     mad        ohlc     resample    tail \n",
      "boxplot    cumprod   first      max        pad      rolling     take \n",
      "\n"
     ]
    }
   ],
   "source": [
    "import IPython\n",
    "\n",
    "# Grouping by one factor\n",
    "df_rank = df.groupby('rank')\n",
    "\n",
    "# Getting all methods from the groupby object:\n",
    "meth = [method_name for method_name in dir(df_rank)\n",
    "     if callable(getattr(df_rank, method_name)) & ~method_name.startswith('_')]\n",
    "\n",
    "# Printing the result\n",
    "print(IPython.utils.text.columnize(meth))"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 11,
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/plain": [
       "{'AssocProf': Int64Index([  6,  11,  25,  40,  42,  55,  56,  58,  59,  61,  64,  66,  90,\n",
       "              92,  93,  97, 105, 107, 108, 109, 112, 124, 131, 133, 139, 141,\n",
       "             142, 154, 157, 159, 163, 169, 175, 177, 178, 183, 187, 189, 194,\n",
       "             195, 196, 215, 218, 219, 223, 228, 232, 256, 258, 261, 285, 286,\n",
       "             294, 300, 317, 322, 323, 329, 335, 364, 368, 371, 380, 383],\n",
       "            dtype='int64'),\n",
       " 'AsstProf': Int64Index([  3,  12,  13,  14,  28,  29,  32,  34,  35,  36,  38,  50,  53,\n",
       "              60,  62,  65,  76,  79,  80,  84,  88,  91,  96, 113, 119, 120,\n",
       "             128, 130, 134, 144, 147, 150, 152, 155, 158, 161, 164, 165, 171,\n",
       "             180, 197, 198, 201, 209, 211, 227, 235, 238, 241, 254, 259, 273,\n",
       "             274, 275, 288, 290, 307, 309, 316, 326, 349, 355, 360, 377, 378,\n",
       "             381, 397],\n",
       "            dtype='int64'),\n",
       " 'Prof': Int64Index([  1,   2,   4,   5,   7,   8,   9,  10,  15,  16,\n",
       "             ...\n",
       "             387, 388, 389, 390, 391, 392, 393, 394, 395, 396],\n",
       "            dtype='int64', length=266)}"
      ]
     },
     "execution_count": 11,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "df_rank.groups"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 12,
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/html": [
       "<div>\n",
       "<style scoped>\n",
       "    .dataframe tbody tr th:only-of-type {\n",
       "        vertical-align: middle;\n",
       "    }\n",
       "\n",
       "    .dataframe tbody tr th {\n",
       "        vertical-align: top;\n",
       "    }\n",
       "\n",
       "    .dataframe thead th {\n",
       "        text-align: right;\n",
       "    }\n",
       "</style>\n",
       "<table border=\"1\" class=\"dataframe\">\n",
       "  <thead>\n",
       "    <tr style=\"text-align: right;\">\n",
       "      <th></th>\n",
       "      <th>discipline</th>\n",
       "      <th>yrs.since.phd</th>\n",
       "      <th>yrs.service</th>\n",
       "      <th>sex</th>\n",
       "      <th>salary</th>\n",
       "    </tr>\n",
       "  </thead>\n",
       "  <tbody>\n",
       "    <tr>\n",
       "      <td>3</td>\n",
       "      <td>B</td>\n",
       "      <td>4</td>\n",
       "      <td>3</td>\n",
       "      <td>Male</td>\n",
       "      <td>79750</td>\n",
       "    </tr>\n",
       "    <tr>\n",
       "      <td>12</td>\n",
       "      <td>B</td>\n",
       "      <td>7</td>\n",
       "      <td>2</td>\n",
       "      <td>Male</td>\n",
       "      <td>79800</td>\n",
       "    </tr>\n",
       "    <tr>\n",
       "      <td>13</td>\n",
       "      <td>B</td>\n",
       "      <td>1</td>\n",
       "      <td>1</td>\n",
       "      <td>Male</td>\n",
       "      <td>77700</td>\n",
       "    </tr>\n",
       "    <tr>\n",
       "      <td>14</td>\n",
       "      <td>B</td>\n",
       "      <td>2</td>\n",
       "      <td>0</td>\n",
       "      <td>Male</td>\n",
       "      <td>78000</td>\n",
       "    </tr>\n",
       "    <tr>\n",
       "      <td>28</td>\n",
       "      <td>B</td>\n",
       "      <td>5</td>\n",
       "      <td>3</td>\n",
       "      <td>Male</td>\n",
       "      <td>82379</td>\n",
       "    </tr>\n",
       "  </tbody>\n",
       "</table>\n",
       "</div>"
      ],
      "text/plain": [
       "   discipline  yrs.since.phd  yrs.service   sex  salary\n",
       "3           B              4            3  Male   79750\n",
       "12          B              7            2  Male   79800\n",
       "13          B              1            1  Male   77700\n",
       "14          B              2            0  Male   78000\n",
       "28          B              5            3  Male   82379"
      ]
     },
     "execution_count": 12,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "df_rank.get_group('AsstProf').head()"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 13,
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/html": [
       "<div>\n",
       "<style scoped>\n",
       "    .dataframe tbody tr th:only-of-type {\n",
       "        vertical-align: middle;\n",
       "    }\n",
       "\n",
       "    .dataframe tbody tr th {\n",
       "        vertical-align: top;\n",
       "    }\n",
       "\n",
       "    .dataframe thead th {\n",
       "        text-align: right;\n",
       "    }\n",
       "</style>\n",
       "<table border=\"1\" class=\"dataframe\">\n",
       "  <thead>\n",
       "    <tr style=\"text-align: right;\">\n",
       "      <th></th>\n",
       "      <th>rank</th>\n",
       "      <th>discipline</th>\n",
       "      <th>yrs.since.phd</th>\n",
       "      <th>yrs.service</th>\n",
       "      <th>sex</th>\n",
       "      <th>salary</th>\n",
       "    </tr>\n",
       "  </thead>\n",
       "  <tbody>\n",
       "    <tr>\n",
       "      <td>1</td>\n",
       "      <td>Prof</td>\n",
       "      <td>B</td>\n",
       "      <td>19</td>\n",
       "      <td>18</td>\n",
       "      <td>Male</td>\n",
       "      <td>139750</td>\n",
       "    </tr>\n",
       "    <tr>\n",
       "      <td>2</td>\n",
       "      <td>Prof</td>\n",
       "      <td>B</td>\n",
       "      <td>20</td>\n",
       "      <td>16</td>\n",
       "      <td>Male</td>\n",
       "      <td>173200</td>\n",
       "    </tr>\n",
       "    <tr>\n",
       "      <td>3</td>\n",
       "      <td>AsstProf</td>\n",
       "      <td>B</td>\n",
       "      <td>4</td>\n",
       "      <td>3</td>\n",
       "      <td>Male</td>\n",
       "      <td>79750</td>\n",
       "    </tr>\n",
       "    <tr>\n",
       "      <td>4</td>\n",
       "      <td>Prof</td>\n",
       "      <td>B</td>\n",
       "      <td>45</td>\n",
       "      <td>39</td>\n",
       "      <td>Male</td>\n",
       "      <td>115000</td>\n",
       "    </tr>\n",
       "    <tr>\n",
       "      <td>5</td>\n",
       "      <td>Prof</td>\n",
       "      <td>B</td>\n",
       "      <td>40</td>\n",
       "      <td>41</td>\n",
       "      <td>Male</td>\n",
       "      <td>141500</td>\n",
       "    </tr>\n",
       "    <tr>\n",
       "      <td>6</td>\n",
       "      <td>AssocProf</td>\n",
       "      <td>B</td>\n",
       "      <td>6</td>\n",
       "      <td>6</td>\n",
       "      <td>Male</td>\n",
       "      <td>97000</td>\n",
       "    </tr>\n",
       "    <tr>\n",
       "      <td>7</td>\n",
       "      <td>Prof</td>\n",
       "      <td>B</td>\n",
       "      <td>30</td>\n",
       "      <td>23</td>\n",
       "      <td>Male</td>\n",
       "      <td>175000</td>\n",
       "    </tr>\n",
       "    <tr>\n",
       "      <td>11</td>\n",
       "      <td>AssocProf</td>\n",
       "      <td>B</td>\n",
       "      <td>12</td>\n",
       "      <td>8</td>\n",
       "      <td>Male</td>\n",
       "      <td>119800</td>\n",
       "    </tr>\n",
       "    <tr>\n",
       "      <td>12</td>\n",
       "      <td>AsstProf</td>\n",
       "      <td>B</td>\n",
       "      <td>7</td>\n",
       "      <td>2</td>\n",
       "      <td>Male</td>\n",
       "      <td>79800</td>\n",
       "    </tr>\n",
       "    <tr>\n",
       "      <td>13</td>\n",
       "      <td>AsstProf</td>\n",
       "      <td>B</td>\n",
       "      <td>1</td>\n",
       "      <td>1</td>\n",
       "      <td>Male</td>\n",
       "      <td>77700</td>\n",
       "    </tr>\n",
       "    <tr>\n",
       "      <td>14</td>\n",
       "      <td>AsstProf</td>\n",
       "      <td>B</td>\n",
       "      <td>2</td>\n",
       "      <td>0</td>\n",
       "      <td>Male</td>\n",
       "      <td>78000</td>\n",
       "    </tr>\n",
       "    <tr>\n",
       "      <td>25</td>\n",
       "      <td>AssocProf</td>\n",
       "      <td>A</td>\n",
       "      <td>13</td>\n",
       "      <td>8</td>\n",
       "      <td>Female</td>\n",
       "      <td>74830</td>\n",
       "    </tr>\n",
       "    <tr>\n",
       "      <td>28</td>\n",
       "      <td>AsstProf</td>\n",
       "      <td>B</td>\n",
       "      <td>5</td>\n",
       "      <td>3</td>\n",
       "      <td>Male</td>\n",
       "      <td>82379</td>\n",
       "    </tr>\n",
       "    <tr>\n",
       "      <td>40</td>\n",
       "      <td>AssocProf</td>\n",
       "      <td>B</td>\n",
       "      <td>9</td>\n",
       "      <td>9</td>\n",
       "      <td>Male</td>\n",
       "      <td>100938</td>\n",
       "    </tr>\n",
       "    <tr>\n",
       "      <td>42</td>\n",
       "      <td>AssocProf</td>\n",
       "      <td>B</td>\n",
       "      <td>23</td>\n",
       "      <td>23</td>\n",
       "      <td>Male</td>\n",
       "      <td>93418</td>\n",
       "    </tr>\n",
       "  </tbody>\n",
       "</table>\n",
       "</div>"
      ],
      "text/plain": [
       "         rank discipline  yrs.since.phd  yrs.service     sex  salary\n",
       "1        Prof          B             19           18    Male  139750\n",
       "2        Prof          B             20           16    Male  173200\n",
       "3    AsstProf          B              4            3    Male   79750\n",
       "4        Prof          B             45           39    Male  115000\n",
       "5        Prof          B             40           41    Male  141500\n",
       "6   AssocProf          B              6            6    Male   97000\n",
       "7        Prof          B             30           23    Male  175000\n",
       "11  AssocProf          B             12            8    Male  119800\n",
       "12   AsstProf          B              7            2    Male   79800\n",
       "13   AsstProf          B              1            1    Male   77700\n",
       "14   AsstProf          B              2            0    Male   78000\n",
       "25  AssocProf          A             13            8  Female   74830\n",
       "28   AsstProf          B              5            3    Male   82379\n",
       "40  AssocProf          B              9            9    Male  100938\n",
       "42  AssocProf          B             23           23    Male   93418"
      ]
     },
     "execution_count": 13,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "df_rank.head()"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 14,
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/html": [
       "<div>\n",
       "<style scoped>\n",
       "    .dataframe tbody tr th:only-of-type {\n",
       "        vertical-align: middle;\n",
       "    }\n",
       "\n",
       "    .dataframe tbody tr th {\n",
       "        vertical-align: top;\n",
       "    }\n",
       "\n",
       "    .dataframe thead th {\n",
       "        text-align: right;\n",
       "    }\n",
       "</style>\n",
       "<table border=\"1\" class=\"dataframe\">\n",
       "  <thead>\n",
       "    <tr style=\"text-align: right;\">\n",
       "      <th></th>\n",
       "      <th>discipline</th>\n",
       "      <th>yrs.since.phd</th>\n",
       "      <th>yrs.service</th>\n",
       "      <th>sex</th>\n",
       "      <th>salary</th>\n",
       "    </tr>\n",
       "    <tr>\n",
       "      <th>rank</th>\n",
       "      <th></th>\n",
       "      <th></th>\n",
       "      <th></th>\n",
       "      <th></th>\n",
       "      <th></th>\n",
       "    </tr>\n",
       "  </thead>\n",
       "  <tbody>\n",
       "    <tr>\n",
       "      <td>AssocProf</td>\n",
       "      <td>64</td>\n",
       "      <td>64</td>\n",
       "      <td>64</td>\n",
       "      <td>64</td>\n",
       "      <td>64</td>\n",
       "    </tr>\n",
       "    <tr>\n",
       "      <td>AsstProf</td>\n",
       "      <td>67</td>\n",
       "      <td>67</td>\n",
       "      <td>67</td>\n",
       "      <td>67</td>\n",
       "      <td>67</td>\n",
       "    </tr>\n",
       "    <tr>\n",
       "      <td>Prof</td>\n",
       "      <td>266</td>\n",
       "      <td>266</td>\n",
       "      <td>266</td>\n",
       "      <td>266</td>\n",
       "      <td>266</td>\n",
       "    </tr>\n",
       "  </tbody>\n",
       "</table>\n",
       "</div>"
      ],
      "text/plain": [
       "           discipline  yrs.since.phd  yrs.service  sex  salary\n",
       "rank                                                          \n",
       "AssocProf          64             64           64   64      64\n",
       "AsstProf           67             67           67   67      67\n",
       "Prof              266            266          266  266     266"
      ]
     },
     "execution_count": 14,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "df_rank.count()"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 15,
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/html": [
       "<div>\n",
       "<style scoped>\n",
       "    .dataframe tbody tr th:only-of-type {\n",
       "        vertical-align: middle;\n",
       "    }\n",
       "\n",
       "    .dataframe tbody tr th {\n",
       "        vertical-align: top;\n",
       "    }\n",
       "\n",
       "    .dataframe thead th {\n",
       "        text-align: right;\n",
       "    }\n",
       "</style>\n",
       "<table border=\"1\" class=\"dataframe\">\n",
       "  <thead>\n",
       "    <tr style=\"text-align: right;\">\n",
       "      <th></th>\n",
       "      <th>rank</th>\n",
       "      <th>discipline</th>\n",
       "      <th>yrs.since.phd</th>\n",
       "      <th>yrs.service</th>\n",
       "      <th>sex</th>\n",
       "      <th>salary</th>\n",
       "    </tr>\n",
       "    <tr>\n",
       "      <th>rank</th>\n",
       "      <th></th>\n",
       "      <th></th>\n",
       "      <th></th>\n",
       "      <th></th>\n",
       "      <th></th>\n",
       "      <th></th>\n",
       "    </tr>\n",
       "  </thead>\n",
       "  <tbody>\n",
       "    <tr>\n",
       "      <td>AssocProf</td>\n",
       "      <td>1</td>\n",
       "      <td>2</td>\n",
       "      <td>24</td>\n",
       "      <td>21</td>\n",
       "      <td>2</td>\n",
       "      <td>63</td>\n",
       "    </tr>\n",
       "    <tr>\n",
       "      <td>AsstProf</td>\n",
       "      <td>1</td>\n",
       "      <td>2</td>\n",
       "      <td>11</td>\n",
       "      <td>7</td>\n",
       "      <td>2</td>\n",
       "      <td>53</td>\n",
       "    </tr>\n",
       "    <tr>\n",
       "      <td>Prof</td>\n",
       "      <td>1</td>\n",
       "      <td>2</td>\n",
       "      <td>42</td>\n",
       "      <td>50</td>\n",
       "      <td>2</td>\n",
       "      <td>261</td>\n",
       "    </tr>\n",
       "  </tbody>\n",
       "</table>\n",
       "</div>"
      ],
      "text/plain": [
       "           rank  discipline  yrs.since.phd  yrs.service  sex  salary\n",
       "rank                                                                \n",
       "AssocProf     1           2             24           21    2      63\n",
       "AsstProf      1           2             11            7    2      53\n",
       "Prof          1           2             42           50    2     261"
      ]
     },
     "execution_count": 15,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "df_rank.nunique()"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 16,
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/html": [
       "<div>\n",
       "<style scoped>\n",
       "    .dataframe tbody tr th:only-of-type {\n",
       "        vertical-align: middle;\n",
       "    }\n",
       "\n",
       "    .dataframe tbody tr th {\n",
       "        vertical-align: top;\n",
       "    }\n",
       "\n",
       "    .dataframe thead th {\n",
       "        text-align: right;\n",
       "    }\n",
       "</style>\n",
       "<table border=\"1\" class=\"dataframe\">\n",
       "  <thead>\n",
       "    <tr style=\"text-align: right;\">\n",
       "      <th></th>\n",
       "      <th>index</th>\n",
       "      <th>N Missing Values</th>\n",
       "    </tr>\n",
       "  </thead>\n",
       "  <tbody>\n",
       "    <tr>\n",
       "      <td>0</td>\n",
       "      <td>rank</td>\n",
       "      <td>44</td>\n",
       "    </tr>\n",
       "    <tr>\n",
       "      <td>1</td>\n",
       "      <td>discipline</td>\n",
       "      <td>41</td>\n",
       "    </tr>\n",
       "    <tr>\n",
       "      <td>2</td>\n",
       "      <td>yrs.since.phd</td>\n",
       "      <td>40</td>\n",
       "    </tr>\n",
       "    <tr>\n",
       "      <td>3</td>\n",
       "      <td>yrs.service</td>\n",
       "      <td>28</td>\n",
       "    </tr>\n",
       "    <tr>\n",
       "      <td>4</td>\n",
       "      <td>sex</td>\n",
       "      <td>45</td>\n",
       "    </tr>\n",
       "    <tr>\n",
       "      <td>5</td>\n",
       "      <td>salary</td>\n",
       "      <td>47</td>\n",
       "    </tr>\n",
       "  </tbody>\n",
       "</table>\n",
       "</div>"
      ],
      "text/plain": [
       "           index  N Missing Values\n",
       "0           rank                44\n",
       "1     discipline                41\n",
       "2  yrs.since.phd                40\n",
       "3    yrs.service                28\n",
       "4            sex                45\n",
       "5         salary                47"
      ]
     },
     "execution_count": 16,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "df_null = df.mask(np.random.random(df.shape) < .1)\n",
    "df_null.isnull().sum().reset_index(name='N Missing Values')"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 17,
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/html": [
       "<div>\n",
       "<style scoped>\n",
       "    .dataframe tbody tr th:only-of-type {\n",
       "        vertical-align: middle;\n",
       "    }\n",
       "\n",
       "    .dataframe tbody tr th {\n",
       "        vertical-align: top;\n",
       "    }\n",
       "\n",
       "    .dataframe thead th {\n",
       "        text-align: right;\n",
       "    }\n",
       "</style>\n",
       "<table border=\"1\" class=\"dataframe\">\n",
       "  <thead>\n",
       "    <tr style=\"text-align: right;\">\n",
       "      <th></th>\n",
       "      <th>rank</th>\n",
       "      <th>discipline</th>\n",
       "      <th>yrs.since.phd</th>\n",
       "      <th>yrs.service</th>\n",
       "      <th>sex</th>\n",
       "      <th>salary</th>\n",
       "    </tr>\n",
       "    <tr>\n",
       "      <th>rank</th>\n",
       "      <th></th>\n",
       "      <th></th>\n",
       "      <th></th>\n",
       "      <th></th>\n",
       "      <th></th>\n",
       "      <th></th>\n",
       "    </tr>\n",
       "  </thead>\n",
       "  <tbody>\n",
       "    <tr>\n",
       "      <td>AssocProf</td>\n",
       "      <td>1</td>\n",
       "      <td>2</td>\n",
       "      <td>19</td>\n",
       "      <td>19</td>\n",
       "      <td>2</td>\n",
       "      <td>53</td>\n",
       "    </tr>\n",
       "    <tr>\n",
       "      <td>AsstProf</td>\n",
       "      <td>1</td>\n",
       "      <td>2</td>\n",
       "      <td>11</td>\n",
       "      <td>7</td>\n",
       "      <td>2</td>\n",
       "      <td>42</td>\n",
       "    </tr>\n",
       "    <tr>\n",
       "      <td>Prof</td>\n",
       "      <td>1</td>\n",
       "      <td>2</td>\n",
       "      <td>41</td>\n",
       "      <td>48</td>\n",
       "      <td>2</td>\n",
       "      <td>200</td>\n",
       "    </tr>\n",
       "  </tbody>\n",
       "</table>\n",
       "</div>"
      ],
      "text/plain": [
       "           rank  discipline  yrs.since.phd  yrs.service  sex  salary\n",
       "rank                                                                \n",
       "AssocProf     1           2             19           19    2      53\n",
       "AsstProf      1           2             11            7    2      42\n",
       "Prof          1           2             41           48    2     200"
      ]
     },
     "execution_count": 17,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "df_null.groupby('rank').nunique()"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 18,
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/html": [
       "<div>\n",
       "<style scoped>\n",
       "    .dataframe tbody tr th:only-of-type {\n",
       "        vertical-align: middle;\n",
       "    }\n",
       "\n",
       "    .dataframe tbody tr th {\n",
       "        vertical-align: top;\n",
       "    }\n",
       "\n",
       "    .dataframe thead th {\n",
       "        text-align: right;\n",
       "    }\n",
       "</style>\n",
       "<table border=\"1\" class=\"dataframe\">\n",
       "  <thead>\n",
       "    <tr style=\"text-align: right;\">\n",
       "      <th></th>\n",
       "      <th>rank</th>\n",
       "      <th>salary</th>\n",
       "    </tr>\n",
       "  </thead>\n",
       "  <tbody>\n",
       "    <tr>\n",
       "      <td>0</td>\n",
       "      <td>AssocProf</td>\n",
       "      <td>93876.437500</td>\n",
       "    </tr>\n",
       "    <tr>\n",
       "      <td>1</td>\n",
       "      <td>AsstProf</td>\n",
       "      <td>80775.985075</td>\n",
       "    </tr>\n",
       "    <tr>\n",
       "      <td>2</td>\n",
       "      <td>Prof</td>\n",
       "      <td>126772.109023</td>\n",
       "    </tr>\n",
       "  </tbody>\n",
       "</table>\n",
       "</div>"
      ],
      "text/plain": [
       "        rank         salary\n",
       "0  AssocProf   93876.437500\n",
       "1   AsstProf   80775.985075\n",
       "2       Prof  126772.109023"
      ]
     },
     "execution_count": 18,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "df_rank['salary'].mean().reset_index()"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": []
  }
 ],
 "metadata": {
  "kernelspec": {
   "display_name": "Python 3",
   "language": "python",
   "name": "python3"
  },
  "language_info": {
   "codemirror_mode": {
    "name": "ipython",
    "version": 3
   },
   "file_extension": ".py",
   "mimetype": "text/x-python",
   "name": "python",
   "nbconvert_exporter": "python",
   "pygments_lexer": "ipython3",
   "version": "3.7.3"
  }
 },
 "nbformat": 4,
 "nbformat_minor": 2
}