count by group in python code example

Example 1: pandas groupby count as new column

In [12]: df.groupby(["item", "color"])["id"].count().reset_index(name="count")
Out[12]:
    item  color  count
0    car  black      2
1  truck   blue      1
2  truck    red      2

Example 2: group by count dataframe

df.groupby(['col1','col2']).size()