DOC: Add Notes about difference to numpy behaviour for ddof in std() GH35985

[timhunderwood]

• closes DOC: make difference between numpy behaviour clearer in Dataframe.std() and Series.std() #35985
• tests added / passed
• passes black pandas
• passes git diff upstream/master -u -- "*.py" | flake8 --diff
• whatsnew entry

[dsaxton]

Thanks @timhunderwood, small suggested wording edit

[MarcoGorelli]

Thanks @timhunderwood

normalizes by N

Are you sure this is correct? Does dividing by N actually normalise the quantity?

IMO it should be enough to write something like

Notes
-----
To have the same behaviour as `numpy.std`, use `ddof=0` (instead of the default `ddof=1`)

[timhunderwood]

Thanks @timhunderwood

normalizes by N

Are you sure this is correct? Does dividing by N actually normalise the quantity?

IMO it should be enough to write something like

Notes
-----
To have the same behaviour as `numpy.std`, use `ddof=0` (instead of the default `ddof=1`)

Thanks @timhunderwood

normalizes by N

Are you sure this is correct? Does dividing by N actually normalise the quantity?

IMO it should be enough to write something like

Notes
-----
To have the same behaviour as `numpy.std`, use `ddof=0` (instead of the default `ddof=1`)

thanks @MarcoGorelli , I agree this could be confusing. I've changed to your simpler wording, thanks.

[dsaxton]

Seems like an improvement to me 👍

[MarcoGorelli]

Looks good to me, can you fetch and merge upstream/master and then push again to restart the CI process in order to get it green?

[timhunderwood]

Looks good to me, can you fetch and merge upstream/master and then push again to restart the CI process in order to get it green?

Done - CI process has started...

[MarcoGorelli]

Thanks @timhunderwood !