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)組楼镐，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)組的返回值宵喂，這樣表示
image.png
image.png
