How to count all values of a one column?

Question

I am trying to count all the instances of all values of col_a

for ex.

col_a
 A
 B
 C
 A
 D
 B
 A

Is there one line of code I can use that would tell me how many times each value (A,B,C,D) exist in that column?

Answer 1

So the solution will be value_counts

df.col_a.value_counts()

Answer 2

Or use groupby with size:

>>> df.groupby('col_a').size()
col_a
A    3
B    2
C    1
D    1
dtype: int64
>>>