Numpy: RMS (root mean squared error) calculation is missing from numpy package

This has been suggested before; generally the consensus is against adding functionality that can be easily composed from existing numpy functions. See #12579 for additional discussion.

Thanks for sharing the idea!

Sorry for asking but what makes 'mean' function different? mean is a very commonly used function which can be simply derived from sum and count. In my opinion, mean is used very frequently to make it a standalone function in numpy. The same stands for pivoting in pandas (I know that is a different package), but pivot_table is also a function that could be implemented by the users again and again by using simple existing functionalities like aggregate, transform, filters, etc.

np.mean already exists.

Please look at the discussion in the issue @rossbar links to, rather than repeating it here.