Pandas: how to apply function to only part of a dataframe and append result back to dataframe?

Question

I've created the following Data Frame

User    Week1  Week2

UserA   5      7
UserB   7      0
UserC   8     20

from this original list

List = [['UserA',5,7],['UserB',7,0],['UserC',8,20]]

I'd like to calculate a formula for each user for every week and create a third column and fourth column of the result for those formulas.

The issue is when I try to do the following, I get a 'TypeError: Could not convert ...to numeric':

    return DF.apply(lambda x: (x - x.mean()) / x.std())

The following method works though:

 Python_Sublists = [subli[1:3] for subli in List]
 >>[[5,7],[7,0],[8,20]]

DF = pd.DataFrame(Python_Sublists,columns=['Week1','Week2'])

return DF.apply(lambda x: (x - x.mean()) / x.std())

I could then figure out how to append these lists back to the original list (though I have no idea how to go from a dataframe to a list again to do this). Is there more of a direct way to only apply the function to the numeric variables? Also, how would you change the pandas dataframe back to its original list form anyway?

Answer 1

Shouldn't df[['week1','week2']].apply(lambda x: (x - x.mean()) / x.std()) work? Your first column is not numerical data. I am sure that is causing the problem.

To 'append' the new one to the original dataframe, if needed, can be simply: df[['c3','c4']]=df[['week1','week2']].apply(lambda x: (x - x.mean()) / x.std()). The new columns will be named 'c3' and 'c4'