Add new column in Pandas DataFrame Python [duplicate]

Question

I have dataframe in Pandas for example:

Col1 Col2 A     1  B     2 C     3 

Now if I would like to add one more column named Col3 and the value is based on Col2. In formula, if Col2 > 1, then Col3 is 0, otherwise would be 1. So, in the example above. The output would be:

Col1 Col2 Col3 A    1    1 B    2    0 C    3    0 

Any idea on how to achieve this?

Answer 1

You just do an opposite comparison. if Col2 <= 1. This will return a boolean Series with False values for those greater than 1 and True values for the other. If you convert it to an int64 dtype, True becomes 1 and False become 0,

df['Col3'] = (df['Col2'] <= 1).astype(int) 

If you want a more general solution, where you can assign any number to Col3 depending on the value of Col2 you should do something like:

df['Col3'] = df['Col2'].map(lambda x: 42 if x > 1 else 55) 

Or:

df['Col3'] = 0 condition = df['Col2'] > 1 df.loc[condition, 'Col3'] = 42 df.loc[~condition, 'Col3'] = 55