How to set DataFrame column values conditionally without a loop in Python

Question

I have the following Pandas DataFrame:

(My original DataFrame is a lot bigger than the one in this example.)

I need to add another column (col3) to this DataFrame and values of col3 will be set based on following conditions:

The above DataFrame will look as the following after this operation:

Is there a way to do this without looping through the DataFrame?

BENY · Accepted Answer · 2020-08-06 20:24:52Z

2

We can do sign from numpy

df['col3']=np.sign((df.col2-df.col1))+1

answered Aug 6, 2020 at 20:24

BENY

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1 Comment

Just great! Thank you!

Quang Hoang · Accepted Answer · 2020-08-06 20:24:41Z

1

You can do np.select:

df['col3'] = np.select((df['col1'] > df['col2'], df['col1'] < df['col2']),
                       (0, 2), 1)

Or use np.sign:

df['col3'] = np.sign(df['col2']-df['col1']) + 1

answered Aug 6, 2020 at 20:24

Quang Hoang

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np.select is a god way as well. Thank you!