numpy.where
numpy.
where
(condition[, x, y])
Return elements, either from x or y, depending on condition.
If only condition is given, return condition.nonzero()
.

Returns:
out : ndarray or tuple of ndarrays
If both x and y are specified, the output array contains elements of xwhere condition is True, and elements from y elsewhere.
If only condition is given, return the tuple condition.nonzero()
, the indices where condition is True.

如果二維數(shù)組數(shù)組使用where的話返回的也是一個二維數(shù)組，準(zhǔn)確的來說一維數(shù)組返回的也是一個二維數(shù)組

x = np.arange(9.).reshape(3, 3)
>>> np.where( x > 5 )
    (array([2, 2, 2]), array([0, 1, 2]))
>>> x[np.where( x > 3.0 )]               # Note: result is 1D.
    array([ 4.,  5.,  6.,  7.,  8.])
>>> np.where(x < 5, x, -1)               # 值替換
    array([[ 0.,  1.,  2.],
           [ 3.,  4., -1.],
           [-1., -1., -1.]])

image.png

(array([2, 2, 2]), array([0, 1, 2]))

第三行的1，2，3列大于五

關(guān)于一維數(shù)組的返回值，這樣表示

image.png

image.png