Return a where condition is True.
If condition is a MaskedArray, missing values are considered as False.
Parameters :  condition : var
axis : {None, int}, optional
out : {None, ndarray}, optional


Returns :  result : MaskedArray

Notes
Please note the difference with compressed ! The output of compress has a mask, the output of compressed does not.
Examples
>>> x = np.ma.array([[1,2,3],[4,5,6],[7,8,9]], mask=[0] + [1,0]*4)
>>> print x
[[1  3]
[ 5 ]
[7  9]]
>>> x.compress([1, 0, 1])
masked_array(data = [1 3],
mask = [False False],
fill_value=999999)
>>> x.compress([1, 0, 1], axis=1)
masked_array(data =
[[1 3]
[ ]
[7 9]],
mask =
[[False False]
[ True True]
[False False]],
fill_value=999999)