Add standard deviation

[oberien]

No description provided.

[LukeMathWalker]

Hi @oberien!

Thanks for the taking the time to draft a PR.
Right now there is a method in ndarray to compute the standard deviation along an axis (std_axis).
Should we add this method here @jturner314 or should we rather move it upstream in ndarray?

[jturner314]

ndarray has sum, sum_axis, mean, mean_axis, std_axis, and var_axis. I think we should add std and var to ndarray for consistency, ideally using the same algorithm as the existing std_axis and var_axis methods and including the same ddof parameter.

[munckymagik]

Did this bit of work move to ndarray then? If so shall we close this to clear the decks?

[LukeMathWalker]

I have opened an issue in ndarray to keep track of it ( rust-ndarray/ndarray#655 ) - we can close here.