Pandas groupby agg - how to get counts?

Question

I am trying to get sum, mean and count of a metric

df.groupby(['id', 'pushid']).agg({"sess_length": [ np.sum, np.mean, np.count]})

But I get "module 'numpy' has no attribute 'count'", and I have tried different ways of expressing the count function but can't get it to work. How do I just an aggregate record count together with the other metrics?

Answer 1

You can use strings instead of the functions, like so:

df = pd.DataFrame(
    {"id": list("ccdef"), "pushid": list("aabbc"), 
     "sess_length": [10, 20, 30, 40, 50]}
)

df.groupby(["id", "pushid"]).agg({"sess_length": ["sum", "mean", "count"]})

Which outputs:

           sess_length
                   sum mean count
 id pushid
 c  a               30   15     2
 d  b               30   30     1
 e  b               40   40     1
 f  c               50   50     1