Adding a column in Pandas with a function

Question

Let's say I have a dataframe like this:

  columnA  columnB
0   10        90
1   83        17
2   30        21
...

and I have a function like this:

def my_func(a, b):
    value = #do some calculation
    return value

Now I want to get a new column columnC for my dataframe based on the calculations of the function.
Obviously, df["columnC"]= my_func(df["columnA"], df["columnB"]) does not work.

What can I do to add the column?

Answer 1

The right way to do it is:

df['c'] = df.apply(lambda row: my_func(row['a'], row['b']), axis=1)

Answer 2

I found a workaround. It's a bit hacky though...

df["columnC"]=pd.Series([my_func(row["columnA"], row["columnB"])for index, row in df.iterrows()], index=df.index)