CODEWITHSUNDEEP
pythonpython-3.xpandas
Palash Tichkule
Palash Tichkule

Reputation: 296

How to set value to a cell filtered by rows in python DataFrame?

import pandas as pd

df = pd.DataFrame([[1,2,3],[4,5,6],[7,8,9],[10,11,12]],columns=['A','B','C'])
df[df['B']%2 ==0]['C'] = 5

I am expecting this code to change the value of columns C to 5, wherever B is even. But it is not working.

It returns the table as follow

    A   B   C
0   1   2   3
1   4   5   6
2   7   8   9
3   10  11  12

I am expecting it to return

    A   B   C
0   1   2   5
1   4   5   6
2   7   8   5
3   10  11  12

Upvotes: 4

Views: 5086

Answers (3)

min2bro
min2bro

Reputation: 4628

Using numpy where

df['C'] = np.where(df['B']%2 == 0, 5, df['C'])

Output

    A   B   C
0   1   2   5
1   4   5   6
2   7   8   5
3   10  11  12

Upvotes: 0

Aryerez
Aryerez

Reputation: 3495

You could just change the order to:

df['C'][df['B']%2 == 0] = 5

And it also works

Upvotes: 0

jezrael
jezrael

Reputation: 862511

If need change value of column in DataFrame is necessary DataFrame.loc with condition and column name:

df.loc[df['B']%2 ==0, 'C'] = 5
print (df)
    A   B   C
0   1   2   5
1   4   5   6
2   7   8   5
3  10  11  12

Your solution is nice example of chained indexing - docs.

Upvotes: 5

Related Questions