count with a function in panda

Question

I am having real fun with groupby function in pandas, please advice on how to apply functions on groupby? Such as, I want to know how many rows grouped by track_id satisfies the rule_1==4 or anything in general.

df.groupby('track_id')['rule_1'].count()

I want to know rule_1 which equals some value.

I tried this - df.groupby('track_id')['rule_1'==4].count()

Is there a callback function or anything simpler ?

Answer 1

Check

df['rule_1'].eq(4).groupby(df['track_id']).sum()