Expressing pandas subset using pipe

Question

I have a dataframe that I subset like this:

   a  b   x  y
0  1  2   3 -1
1  2  4   6 -2
2  3  6   6 -3
3  4  8   3 -4

df = df[(df.a >= 2) & (df.b <=          


        

Answer 1

I believe this method is clear with regard to your filtering steps and subsequent operations. Using loc[(mask1) & (mask2)] is probably more performant, however.

>>> (df
     .pipe(lambda x: x.loc[x.a >= 2])
     .pipe(lambda x: x.loc[x.b <= 8])
     .pipe(pd.DataFrame.groupby, 'x')
     .mean()
     )

     a  b    y
x             
3  4.0  8 -4.0
6  2.5  5 -2.5

Alternatively:

(df
 .pipe(lambda x: x.loc[x.a >= 2])
 .pipe(lambda x: x.loc[x.b <= 8])
 .groupby('x')
 .mean()
 )