numpy.ma.where()

numpy.ma.where(condition, x=, y=) [source]

Return a masked array with elements from x or y, depending on condition.

Returns a masked array, shaped like condition, where the elements are from x when condition is True, and from y otherwise. If neither x nor y are given, the function returns a tuple of indices where condition is True (the result of condition.nonzero()).

Parameters:

Parameters:	condition : array_like, bool The condition to meet. For each True element, yield the corresponding element from `x`, otherwise from `y`. x, y : array_like, optional Values from which to choose. `x` and `y` need to have the same shape as condition, or be broadcast-able to that shape.
Returns:	out : MaskedArray or tuple of ndarrays The resulting masked array if `x` and `y` were given, otherwise the result of `condition.nonzero()`.

condition : array_like, bool

The condition to meet. For each True element, yield the corresponding element from x, otherwise from y.

x, y : array_like, optional

Values from which to choose. x and y need to have the same shape as condition, or be broadcast-able to that shape.

Returns:

out : MaskedArray or tuple of ndarrays

The resulting masked array if x and y were given, otherwise the result of condition.nonzero().

Examples

>>> x = np.ma.array(np.arange(9.).reshape(3, 3), mask=[[0, 1, 0],
...                                                    [1, 0, 1],
...                                                    [0, 1, 0]])
>>> print(x)
[[0.0 -- 2.0]
 [-- 4.0 --]
 [6.0 -- 8.0]]
>>> np.ma.where(x > 5)    # return the indices where x > 5
(array([2, 2]), array([0, 2]))

>>> print(np.ma.where(x > 5, x, -3.1416))
[[-3.1416 -- -3.1416]
 [-- -3.1416 --]
 [6.0 -- 8.0]]

Links:

https://docs.scipy.org/doc/numpy-1.11.0/reference/generated/numpy.ma.where.html

doc_NumPy

2017-01-10 18:15:54

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