how to count a rows by column values in pandas code example

Example 1: number of times a value occurs in dataframne

df['a'].value_counts()

Example 2: pandas count number of rows with value

In [37]:
df = pd.DataFrame({'a':list('abssbab')})
df.groupby('a').count()

Out[37]:

   a
a   
a  2
b  3
s  2

[3 rows x 1 columns]