How to apply a function to two columns of Pandas dataframe

Question

Suppose I have a df which has columns of \'ID\', \'col_1\', \'col_2\'. And I define a function :

f = lambda x, y : my_function_expres

Answer 1

The way you have written f it needs two inputs. If you look at the error message it says you are not providing two inputs to f, just one. The error message is correct.
The mismatch is because df[['col1','col2']] returns a single dataframe with two columns, not two separate columns.

You need to change your f so that it takes a single input, keep the above data frame as input, then break it up into x,y inside the function body. Then do whatever you need and return a single value.

You need this function signature because the syntax is .apply(f) So f needs to take the single thing = dataframe and not two things which is what your current f expects.

Since you haven't provided the body of f I can't help in anymore detail - but this should provide the way out without fundamentally changing your code or using some other methods rather than apply