Find length of longest string in Pandas dataframe column

Question

Is there a faster way to find the length of the longest string in a Pandas DataFrame than what\'s shown in the example below?

import numpy as np
import panda         


        

Answer 1

Excellent answers, in particular Marius and Ricky which were very helpful.

Given that most of us are optimising for coding time, here is a quick extension to those answers to return all the columns' max item length as a series, sorted by the maximum item length per column:

mx_dct = {c: df[c].map(lambda x: len(str(x))).max() for c in df.columns}
pd.Series(mx_dct).sort_values(ascending =False)

Or as a one liner:

pd.Series({c: df[c].map(lambda x: len(str(x))).max() for c in df).sort_values(ascending =False)

Adapting the original sample, this can be demoed as:

import pandas as pd

x = [['ab', 'bcd'], ['dfe', 'efghik']]
df = pd.DataFrame(x, columns=['col1','col2'])

print(pd.Series({c: df[c].map(lambda x: len(str(x))).max() for c in df}).sort_values(ascending =False))

Output:

col2    6
col1    3
dtype: int64