Pandas: create two new columns in a dataframe with values calculated from a pre-existing column

Question

I am working with the pandas library and I want to add two new columns to a dataframe df with n columns (n > 0).

These new columns result from the application of a function to one of the columns in the dataframe.

The function to apply is like:

def calculate(x):

    ...operate...

    return z, y

One method for creating a new column for a function returning only a value is:

df['new_col']) = df['column_A'].map(a_function)

So, what I want, and tried unsuccesfully (*), is something like:

(df['new_col_zetas'], df['new_col_ys']) = df['column_A'].map(calculate)

What the best way to accomplish this could be ? 

**df['column_A'].map(calculate) returns a pandas Series each item consisting of a tuple z, y. And trying to assign this to two dataframe columns produces a ValueError.*

Answer 1

Simply use zip:

In [1]: from pandas import *

In [2]: def calculate(x):

   ...:     return x*2, x*3

   ...: 

In [3]: df = DataFrame({'a': [1,2,3], 'b': [2,3,4]})

In [4]: df

Out[4]: 

   a  b

0  1 2

1  2 3

2  3 4

In [5]: df["A1"], df["A2"] = zip(*df["a"].map(calculate))

In [6]: df

Out[6]: 

   a  b A1  A2

0  1 2   2 3

1  2 3   4 6

2  3 4   6 9