How To Conditionally Update Dataframe Column In Pandas Based On List

Supposed I have a dataframe with one column: df = pd.DataFrame(np.random.randint(0,9,size=(100, 1)), columns=['number']) I have two lists, one list containing even numbers, the ot

Solution 1:

I think you can use numpy.where:

import pandas as pd
import numpy as np

df = pd.DataFrame(np.random.randint(0,9,size=(100, 1)), columns=['number'])

df['odd_or_even'] = np.where(df.number % 2, 'odd', 'even')
print (df)

    number odd_or_even
01         odd
10        even
24        even
35         odd
40        even
50        even
61         odd
70        even
87         odd
98        even

EDIT by comment

Use loc:

import pandas as pd
import numpy as np

df = pd.DataFrame(np.random.randint(0,9,size=(20, 1)), columns=['number'])

odd_numbers = [1,3,5,7,9]
even_numbers = [0,2,4,6,8]

df.loc[df.number.isin(odd_numbers), 'odd_or_even'] = 'odd'
df.loc[df.number.isin(even_numbers), 'odd_or_even'] = 'even'print (df)
    number odd_or_even
05         odd
11         odd
22        even
33         odd
45         odd
56        even
63         odd
74        even
82        even
98        even
108        even
111         odd
122        even
131         odd
143         odd
153         odd
165         odd
174        even
182        even
195         odd

Solution 2:

A map version:

First, create a dictionary:

d = {**{o: "odd" for o in odd_numbers}, **{e: "even" for e in even_numbers}}

Then use map on the series:

df['odd_or_even'] = df['number'].map(d)