Pandas Apply Function - Syntax for row filtering

Question

Similar to a previous question, I need to use the apply function to some data after using groupBy.

Suppose we have the following dataset with column heads A,B,C:

and the following group by is applied:

   mydf=df.groupby(['A','B'])['C'].max()

I need to filter the group by result by a filter to show only those where C is 3, but get an error.

       print(mydf.apply(lambda g: g[g['C'] == 3]))

Thank you in advance.

anky · Accepted Answer · 2020-03-07 04:54:45Z

1

You can use .loc[] with a lambda here:

df.groupby(['A','B'])['C'].max().loc[lambda x: x==3]

A  B
a  0    3
b  0    3
Name: C, dtype: int64

answered Mar 7, 2020 at 4:54

anky

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2 Comments

User 19826 Over a year ago

thank you, I accepted the answer. If you don't mind, could you also tell me how to apply the same filter on either A or B, after performing the group function?

anky Over a year ago

@Fabiana you can reset the index and use loc example: df.groupby(['A','B'])['C'].max().reset_index().loc[lambda x:x['A']=='a'] which will filter column A equal to a for the grouped value

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