GROUP BY SUM ON pandas data frame

Question

df:

a b class
0 0  +
0 1  +
1 0  -

expected output:

group each column based on class value and find the count, 
as in taking column 'a' as example the count should be 2 
for class '+' and 1 for class '-'

Code:

grp = df.groupby(df.class, axis=1).sum()

getting errors which I dont even understand. new to pandas, any suggestions would be great.

Answer 1

尝试这个：

print(sample.groupby('class').count())