`numpy.ma.core:compress`

Signature

def compress ( self , condition , axis = None , out = None )

Return a where condition is True.

If condition is a MaskedArray, missing values are considered as False.

condition : var: Boolean 1-d array selecting which entries to return. If len(condition) is less than the size of a along the axis, then output is truncated to length of condition array.
axis : {None, int}, optional: Axis along which the operation must be performed.
out : {None, ndarray}, optional: Alternative output array in which to place the result. It must have the same shape as the expected output but the type will be cast if necessary.

Please note the difference with compressed ! The output of compress has a mask, the output of compressed does not.

import numpy as np
x = np.ma.array([[1,2,3],[4,5,6],[7,8,9]], mask=[0] + [1,0]*4)
x
x.compress([1, 0, 1])

x.compress([1, 0, 1], axis=1)