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 ? I scanned the documentation with no clue.
**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.*
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Answer
I’d just 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