There are many ways to solve this problem:
Use groupby() and count() functions:
In [37]:
df = pd.DataFrame({'a':list('abssbab')})
df.groupby('a').count()
Out[37]:
a a
a 2
b 3
s 2
Use value_counts() method:
In [38]:
df['a'].value_counts()
Out[38]:
b 3
a 2
s 2
dtype: int64
Use transform() method:
In [41]:
df['freq'] = df.groupby('a')['a'].transform('count')
df
Out[41]:
a freq
0 a 2
1 b 3
2 s 2
3 s 2
4 b 3
5 a 2
6 b 3
Hope this answer helps.
