pandas groupby 分组取每组的前几行记录

╰半橙微兮° 2022-06-01 08:27 286阅读 0赞

直接上例子。

import pandas as pd
    df = pd.DataFrame({'class':['a','a','b','b','a','a','b','c','c'],'score':[3,5,6,7,8,9,10,11,14]})

df:

<table style=""> 
 <thead style=""> 
  <tr style="border:1px solid black; border-collapse:collapse; margin:1em 2em; text-align:right"> 
   <th style="padding:4px; text-align:left; border:1px solid black; border-collapse:collapse; margin:1em 2em; vertical-align:middle; font-weight:bold"> &nbsp;</th> 
   <th style="padding:4px; text-align:left; border:1px solid black; border-collapse:collapse; margin:1em 2em; vertical-align:middle; font-weight:bold"> class</th> 
   <th style="padding:4px; text-align:left; border:1px solid black; border-collapse:collapse; margin:1em 2em; vertical-align:middle; font-weight:bold"> score</th> 
  </tr> 
 </thead> 
 <tbody style=""> 
  <tr style="border:1px solid black; border-collapse:collapse; margin:1em 2em"> 
   <th style="padding:4px; text-align:left; border:1px solid black; border-collapse:collapse; margin:1em 2em; vertical-align:middle; font-weight:bold"> 0</th> 
   <td style="padding:4px; border:1px solid black; border-collapse:collapse; margin:1em 2em; text-align:left; vertical-align:middle"> a</td> 
   <td style="padding:4px; border:1px solid black; border-collapse:collapse; margin:1em 2em; text-align:left; vertical-align:middle"> 3</td> 
  </tr> 
  <tr style="border:1px solid black; border-collapse:collapse; margin:1em 2em"> 
   <th style="padding:4px; text-align:left; border:1px solid black; border-collapse:collapse; margin:1em 2em; vertical-align:middle; font-weight:bold"> 1</th> 
   <td style="padding:4px; border:1px solid black; border-collapse:collapse; margin:1em 2em; text-align:left; vertical-align:middle"> a</td> 
   <td style="padding:4px; border:1px solid black; border-collapse:collapse; margin:1em 2em; text-align:left; vertical-align:middle"> 5</td> 
  </tr> 
  <tr style="border:1px solid black; border-collapse:collapse; margin:1em 2em"> 
   <th style="padding:4px; text-align:left; border:1px solid black; border-collapse:collapse; margin:1em 2em; vertical-align:middle; font-weight:bold"> 2</th> 
   <td style="padding:4px; border:1px solid black; border-collapse:collapse; margin:1em 2em; text-align:left; vertical-align:middle"> b</td> 
   <td style="padding:4px; border:1px solid black; border-collapse:collapse; margin:1em 2em; text-align:left; vertical-align:middle"> 6</td> 
  </tr> 
  <tr style="border:1px solid black; border-collapse:collapse; margin:1em 2em"> 
   <th style="padding:4px; text-align:left; border:1px solid black; border-collapse:collapse; margin:1em 2em; vertical-align:middle; font-weight:bold"> 3</th> 
   <td style="padding:4px; border:1px solid black; border-collapse:collapse; margin:1em 2em; text-align:left; vertical-align:middle"> b</td> 
   <td style="padding:4px; border:1px solid black; border-collapse:collapse; margin:1em 2em; text-align:left; vertical-align:middle"> 7</td> 
  </tr> 
  <tr style="border:1px solid black; border-collapse:collapse; margin:1em 2em"> 
   <th style="padding:4px; text-align:left; border:1px solid black; border-collapse:collapse; margin:1em 2em; vertical-align:middle; font-weight:bold"> 4</th> 
   <td style="padding:4px; border:1px solid black; border-collapse:collapse; margin:1em 2em; text-align:left; vertical-align:middle"> a</td> 
   <td style="padding:4px; border:1px solid black; border-collapse:collapse; margin:1em 2em; text-align:left; vertical-align:middle"> 8</td> 
  </tr> 
  <tr style="border:1px solid black; border-collapse:collapse; margin:1em 2em"> 
   <th style="padding:4px; text-align:left; border:1px solid black; border-collapse:collapse; margin:1em 2em; vertical-align:middle; font-weight:bold"> 5</th> 
   <td style="padding:4px; border:1px solid black; border-collapse:collapse; margin:1em 2em; text-align:left; vertical-align:middle"> a</td> 
   <td style="padding:4px; border:1px solid black; border-collapse:collapse; margin:1em 2em; text-align:left; vertical-align:middle"> 9</td> 
  </tr> 
  <tr style="border:1px solid black; border-collapse:collapse; margin:1em 2em"> 
   <th style="padding:4px; text-align:left; border:1px solid black; border-collapse:collapse; margin:1em 2em; vertical-align:middle; font-weight:bold"> 6</th> 
   <td style="padding:4px; border:1px solid black; border-collapse:collapse; margin:1em 2em; text-align:left; vertical-align:middle"> b</td> 
   <td style="padding:4px; border:1px solid black; border-collapse:collapse; margin:1em 2em; text-align:left; vertical-align:middle"> 10</td> 
  </tr> 
  <tr style="border:1px solid black; border-collapse:collapse; margin:1em 2em"> 
   <th style="padding:4px; text-align:left; border:1px solid black; border-collapse:collapse; margin:1em 2em; vertical-align:middle; font-weight:bold"> 7</th> 
   <td style="padding:4px; border:1px solid black; border-collapse:collapse; margin:1em 2em; text-align:left; vertical-align:middle"> c</td> 
   <td style="padding:4px; border:1px solid black; border-collapse:collapse; margin:1em 2em; text-align:left; vertical-align:middle"> 11</td> 
  </tr> 
  <tr style="border:1px solid black; border-collapse:collapse; margin:1em 2em"> 
   <th style="padding:4px; text-align:left; border:1px solid black; border-collapse:collapse; margin:1em 2em; vertical-align:middle; font-weight:bold"> 8</th> 
   <td style="padding:4px; border:1px solid black; border-collapse:collapse; margin:1em 2em; text-align:left; vertical-align:middle"> c</td> 
   <td style="padding:4px; border:1px solid black; border-collapse:collapse; margin:1em 2em; text-align:left; vertical-align:middle"> 14</td> 
  </tr> 
 </tbody> 
</table>

df.sort_values(['class','score'],ascending=[1,0],inplace=True)
    grouped = df.groupby(['class']).head(2)

grouped:

<table style=""> 
 <thead style=""> 
  <tr style="border:1px solid black; border-collapse:collapse; margin:1em 2em; text-align:right"> 
   <th style="padding:4px; text-align:left; border:1px solid black; border-collapse:collapse; margin:1em 2em; vertical-align:middle; font-weight:bold"> &nbsp;</th> 
   <th style="padding:4px; text-align:left; border:1px solid black; border-collapse:collapse; margin:1em 2em; vertical-align:middle; font-weight:bold"> class</th> 
   <th style="padding:4px; text-align:left; border:1px solid black; border-collapse:collapse; margin:1em 2em; vertical-align:middle; font-weight:bold"> score</th> 
  </tr> 
 </thead> 
 <tbody style=""> 
  <tr style="border:1px solid black; border-collapse:collapse; margin:1em 2em"> 
   <th style="padding:4px; text-align:left; border:1px solid black; border-collapse:collapse; margin:1em 2em; vertical-align:middle; font-weight:bold"> 5</th> 
   <td style="padding:4px; border:1px solid black; border-collapse:collapse; margin:1em 2em; text-align:left; vertical-align:middle"> a</td> 
   <td style="padding:4px; border:1px solid black; border-collapse:collapse; margin:1em 2em; text-align:left; vertical-align:middle"> 9</td> 
  </tr> 
  <tr style="border:1px solid black; border-collapse:collapse; margin:1em 2em"> 
   <th style="padding:4px; text-align:left; border:1px solid black; border-collapse:collapse; margin:1em 2em; vertical-align:middle; font-weight:bold"> 4</th> 
   <td style="padding:4px; border:1px solid black; border-collapse:collapse; margin:1em 2em; text-align:left; vertical-align:middle"> a</td> 
   <td style="padding:4px; border:1px solid black; border-collapse:collapse; margin:1em 2em; text-align:left; vertical-align:middle"> 8</td> 
  </tr> 
  <tr style="border:1px solid black; border-collapse:collapse; margin:1em 2em"> 
   <th style="padding:4px; text-align:left; border:1px solid black; border-collapse:collapse; margin:1em 2em; vertical-align:middle; font-weight:bold"> 6</th> 
   <td style="padding:4px; border:1px solid black; border-collapse:collapse; margin:1em 2em; text-align:left; vertical-align:middle"> b</td> 
   <td style="padding:4px; border:1px solid black; border-collapse:collapse; margin:1em 2em; text-align:left; vertical-align:middle"> 10</td> 
  </tr> 
  <tr style="border:1px solid black; border-collapse:collapse; margin:1em 2em"> 
   <th style="padding:4px; text-align:left; border:1px solid black; border-collapse:collapse; margin:1em 2em; vertical-align:middle; font-weight:bold"> 3</th> 
   <td style="padding:4px; border:1px solid black; border-collapse:collapse; margin:1em 2em; text-align:left; vertical-align:middle"> b</td> 
   <td style="padding:4px; border:1px solid black; border-collapse:collapse; margin:1em 2em; text-align:left; vertical-align:middle"> 7</td> 
  </tr> 
  <tr style="border:1px solid black; border-collapse:collapse; margin:1em 2em"> 
   <th style="padding:4px; text-align:left; border:1px solid black; border-collapse:collapse; margin:1em 2em; vertical-align:middle; font-weight:bold"> 8</th> 
   <td style="padding:4px; border:1px solid black; border-collapse:collapse; margin:1em 2em; text-align:left; vertical-align:middle"> c</td> 
   <td style="padding:4px; border:1px solid black; border-collapse:collapse; margin:1em 2em; text-align:left; vertical-align:middle"> 14</td> 
  </tr> 
  <tr style="border:1px solid black; border-collapse:collapse; margin:1em 2em"> 
   <th style="padding:4px; text-align:left; border:1px solid black; border-collapse:collapse; margin:1em 2em; vertical-align:middle; font-weight:bold"> 7</th> 
   <td style="padding:4px; border:1px solid black; border-collapse:collapse; margin:1em 2em; text-align:left; vertical-align:middle"> c</td> 
   <td style="padding:4px; border:1px solid black; border-collapse:collapse; margin:1em 2em; text-align:left; vertical-align:middle"> 11</td> 
  </tr> 
 </tbody> 
</table>