Counting non zero values in each column of a dataframe in python

Question

I have a python-pandas-dataframe in which first column is user_id and rest of the columns are tags(tag_0 to tag_122). I have the data in the following format:

Answer 1

My favorite way of getting number of nonzeros in each column is

df.astype(bool).sum(axis=0)

For the number of non-zeros in each row use

df.astype(bool).sum(axis=1)

(Thanks to Skulas)

If you have nans in your df you should make these zero first, otherwise they will be counted as 1.

df.fillna(0).astype(bool).sum(axis=1)

(Thanks to SirC)