How to ignore max and min of rows when applying describe function to pandas groupby

Question

I am using pandas groupby function and trying to get the description of the grouped results, but without each group's maximum and minimum row. I can't find the right answer to my question.

data = {'class': ['a', 'a', 'a', 'a', 'a', 'b', 'b', 'b', 'b', 'b'],
       'num': [-10,18,12,15,50, 10,60,51,54,100]}
df = pd.DataFrame(data)
df.groupby('class').describe()

output:

         num
        count   mean    std        min    25%    50%     75%    max
class                               
a      5.0     17.0   21.494185   -10.0   12.0    15.0  18.0    50.0
b      5.0     55.0   31.984371    10.0   51.0    54.0  60.0    100.0

The result that I want is:

       num       
       count    mean    std         min     25%     50%     75%  max
class                               
a      3.0      15.0    3.000000    12.0    13.5    15.0    16.5    18.0
b      3.0      55.0    4.582576    51.0    52.5    54.0    57.0    60.0

Answer 1

Using transform and masking:

df['max']=df.groupby('class')['num'].transform('max')
df['min']=df.groupby('class')['num'].transform('min')

mask = df['num'].ne(df['min'])&df['num'].ne(df['max'])

df.loc[mask,:].groupby('class')['num'].describe()

       count  mean       std   min   25%   50%   75%   max
class                                                     
a        3.0  15.0  3.000000  12.0  13.5  15.0  16.5  18.0
b        3.0  55.0  4.582576  51.0  52.5  54.0  57.0  60.0

Or:

df.loc[mask, ['class', 'num']].groupby('class').describe()
        num                                              
      count  mean       std   min   25%   50%   75%   max
class                                                    
a       3.0  15.0  3.000000  12.0  13.5  15.0  16.5  18.0
b       3.0  55.0  4.582576  51.0  52.5  54.0  57.0  60.0

Answer 2

Another method using apply() , idxmax() and idxmin()

>>df.groupby('class').apply(lambda x: x.drop([x['num'].idxmax(),x['num'].idxmin()])).rename_axis([None,None]).groupby('class').describe()

     num
     count mean std         min    25%     50%      75%     max
class                               
a   3.0   15.0  3.000000    12.0    13.5    15.0    16.5    18.0
b   3.0   55.0  4.582576    51.0    52.5    54.0    57.0    60.0

Explaination: Do a groupby on class and remove max and min values index from each group. then do a groupby on class and call the describe() function.