计算熊猫DF列子集的均值或方差

Question

I have a gigantic pandas DF with a bunch of columns in it. I want to calculate mean and variance for a subset of three columns. Is there an easy way to do this without creating a whole new dataframe? I get all NaN whenever I try to use something like this:

DF['means']=np.mean(DF.A, DF.B, DF.C)

or

DF['means']=DF[['A','B','C','D']].mean(axis=0)

Thanks!

Answer 1

It's not totally clear what exactly you want to do, but it looks like what you mean is taking the per-row average of columns AD. In which case, you're just giving the wrong axis argument.

DF['means']=DF[['A','B','C','D']].mean(axis=1) should work fine.