assign three values based on condition to pandas df column

Question

I have a pandas df that contains a column of positive, negative nos and zeros. I wanted to crate another column which is 1 if no is > 0, -1 if no is < 0 and 0 if the number is 0.

I am trying to do this using a for loop for each row but it is taking too long. I wanted to know if there was a faster way to do this. I also wanted to know if the same logic could be extended to positive and negative timedelta objects.
Thank you.

My final df should look like this:

df = pd.DataFrame({'a':[1, 2, -1, 0, -2], 'b':[1, 1, -1, 0, -1]})

     a   b
0    1   1
1    2   1
2   -1  -1
3    0   0
4   -2  -1

where b is the col to assign based on values of a

BENY · Accepted Answer · 2019-08-02 15:31:42Z

3

Here is one way numpy sign

np.sign(df.a)
Out[118]: 
0    1
1    1
2   -1
3    0
4   -1
Name: a, dtype: int64
df['b'] = np.sign(df.a)

answered Aug 2, 2019 at 15:31

BENY

324k22 gold badges176 silver badges250 bronze badges

Sign up to request clarification or add additional context in comments.

3 Comments

Moshee Over a year ago

Thanks. Is there any way to do this for timedelta objects. I tried it but it doesn't work

BENY Over a year ago

@Moshee np.sign( (df.a / np.timedelta64(1, 'D')).astype(int))

BENY Over a year ago

@Moshee more info stackoverflow.com/questions/25646200/…

Community · Accepted Answer · 2020-06-20 09:12:55Z

2

try using np.where and provide conditions

import numpy as np

df['b']= np.where(df['a']>0,1,
         np.where(df['a']<0,-1,0))

Solution by @rafaelc

m1= df['a'] >0
m2= df['a'] <0


df['b'] = np.select([m1, m2],
                    [ 1, -1], 
                    default=0)

edited Jun 20, 2020 at 9:12

CommunityBot

11 silver badge

answered Aug 2, 2019 at 15:33

tawab_shakeel

3,75912 silver badges26 bronze badges

4 Comments

rafaelc Over a year ago

For multiple conditions, prefer np.select instead of nested np.where

BENY Over a year ago

let me modify a little

tawab_shakeel Over a year ago

@rafaelc thanks for the suggestion .I have add np.select

tawab_shakeel Over a year ago

@WeNYoBen thanks I actually don't use np.select more so that's why I was not familiar with default

Collectives™ on Stack Overflow

assign three values based on condition to pandas df column

2 Answers 2

3 Comments

Solution by @rafaelc

4 Comments

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

3 Comments

Solution by @rafaelc

4 Comments

Your Answer

Sign up or log in

Post as a guest

Linked

Related