Creating Dataframe column using apply() in Python

Question

Say you have a Table T with Columns A and B with numerical values. I want to create a new column C that gives me the ratio of A/B. I know the easy way to do this.

T['C']=T['A']/T['B']

But I want to try using the apply() function to a new copy of Table T. I have the following function below to execute this for any tables.

def ratio(T):
    X=T.copy()
    def ratio(a,b):
        return a/b
    X['C']=X['C'].apply(ratio,'A','B')
    return X

I get the KeyError: 'C' error. How do I properly get 'C' to exist in order to apply it/

Evan Nowak · Accepted Answer · 2017-10-03 04:07:19Z

1

You could simplify this with lambda:

X = T.copy()

X['C'] = T.apply(lambda row: row.A/row.B, axis=1)

answered Oct 3, 2017 at 4:07

Evan Nowak

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