There's a choice we need to make here. Right now (and before this patch), np.ma.sort sometimes returns an ma.array, and sometimes an ndarray.

Should we change it to always promote to ma.array, for consistency with the other functions? (Which do this as of #8665 )

In theory we could do a little better here, by implementing the in-place sort in terms of the non-in place. Right now (and before this patch), the latter does a redundant copy. So either way, best left for another PR, I think

endwith needs to be after fill_value to not break the api

changing axis default also probably breaks api

Not changing it breaks liskov substitution though. The default values should really match ndarray. Fair call on swapping argument order

it would be nice if they matched but unfortunately that ship has sailed, this default argument is part of our api and we can't change it.

@juliantaylor: Is there a deprecation path for changing it then?

Regarding named argument order, perhaps we should enforce that endwith is a boolean, just to help guard against someone (stupidly) passing unnamed arguments, and assuming they match the order of sort?

I don't see a way we could deprecate the axis argument value besides adding an argsort2 and deprecating the old one.

sort has a different order? that is unfortunate ...
I guess we could try to get away with that change, usage of positional arguments for the ones at the end are probably not very common in the wild.

Also, argsort is documented as having a default argument of -1, even though the actual default is None. So can we update the API to match the documentation?

Re deprecation:

if axis is np._NoValue:
    if  self.ndim > 1:
        warn("Unlike np.argsort and the documentation for this function, the"
             "default axis argument is None, not -1. This only matters for 2 or"
             "higher-dimensional arrays. If this is intended, pass it explicitly to squash this warning")
    axis = None

I don't really like these shortcuts very much, the explicit meshgrid is easier to read imo
there isn't really an advantage to using ix_ is there?

Is this really a shortcut though? The two functions are independant, with neither calling the other. Meshgrid doesn't do what we need by default, but ix_ does.

Furthermore, ix_ is used as an indexer in its examples, whereas meshgrid is used to evaluate functions. The former use is what we want here.