How do I count the values from a pandas column which is a list of strings?

Question

I have a dataframe column which is a list of strings:

df[\'colors\']

0              [\'blue\',\'green\',\'brown\']
1              []
2              [\'green\         


        

Answer 1

Use a Counter + chain, which is meant to do exactly this. Then construct the Series from the Counter object.

import pandas as pd
from collections import Counter
from itertools import chain

s = pd.Series([['blue','green','brown'], [], ['green','red','blue']])

pd.Series(Counter(chain.from_iterable(s)))
#blue     2
#green    2
#brown    1
#red      1
#dtype: int64

---

While explode + value_counts are the pandas way to do things, they're slower for shorter lists.

import perfplot
import pandas as pd
import numpy as np

from collections import Counter
from itertools import chain

def counter(s):
    return pd.Series(Counter(chain.from_iterable(s)))

def explode(s):
    return s.explode().value_counts()

perfplot.show(
    setup=lambda n: pd.Series([['blue','green','brown'], [], ['green','red','blue']]*n), 
    kernels=[
        lambda s: counter(s),
        lambda s: explode(s),
    ],
    labels=['counter', 'explode'],
    n_range=[2 ** k for k in range(17)],
    equality_check=np.allclose,  
    xlabel='~len(s)'
)