np.copy(masked array) has unexpected behavior

…where “unexpected” means I didn’t expect it. This may just be a documentation fix, or maybe I will be scolded for not realizing how np.ma works, but I don’t think this behavior is appropriate:

In [100]: x = np.ma.ones(5)

In [101]: x.mask = [False,False,True,False,False]

In [102]: np.copy(x)
Out[102]: array([ 1.,  1.,  1.,  1.,  1.])

In [103]: np.ma.copy(x)
Out[103]:
masked_array(data = [1.0 1.0 -- 1.0 1.0],
             mask = [False False  True False False],
       fill_value = 1e+20)

In [104]: np.__version__
Out[104]: '1.8.0.dev-074a40c'

I would at least expect a warning, but would prefer to see, in order of preference:

• np.copy(x) returns a masked array (since x is a masked array)
• np.copy(x) warns that it is unmasking the array, then returns the same array as above
• np.copy(x) raises an exception
• np.copy(x) returns [1,1,nan,1,1] (this is probably not ideal)

[jjhelmus]

I’ll send an email to the list on the topic tomorrow.

[jjhelmus]

Created PR #6509 which adds a subok parameter to the function with a default value of False. I’m guessing this will open up some discussion on the topic. Not sure if this typically takes place on the PR, the issue, or the mailing list.