Question

我想在选定的轴上用0填充numpy张量。例如，我有张量r形状(4,3,2)，但我只对填充最后两个轴（即仅填充矩阵）感兴趣。是否可以使用单行python代码？

Answer 1

您可以使用np.pad()：

a = np.ones((4, 3, 2))

# npad is a tuple of (n_before, n_after) for each dimension
npad = ((0, 0), (1, 2), (2, 1))
b = np.pad(a, pad_width=npad, mode='constant', constant_values=0)

print(b.shape)
# (4, 6, 5)

print(b)
# [[[ 0.  0.  0.  0.  0.]
#   [ 0.  0.  1.  1.  0.]
#   [ 0.  0.  1.  1.  0.]
#   [ 0.  0.  1.  1.  0.]
#   [ 0.  0.  0.  0.  0.]
#   [ 0.  0.  0.  0.  0.]]

#  [[ 0.  0.  0.  0.  0.]
#   [ 0.  0.  1.  1.  0.]
#   [ 0.  0.  1.  1.  0.]
#   [ 0.  0.  1.  1.  0.]
#   [ 0.  0.  0.  0.  0.]
#   [ 0.  0.  0.  0.  0.]]

#  [[ 0.  0.  0.  0.  0.]
#   [ 0.  0.  1.  1.  0.]
#   [ 0.  0.  1.  1.  0.]
#   [ 0.  0.  1.  1.  0.]
#   [ 0.  0.  0.  0.  0.]
#   [ 0.  0.  0.  0.  0.]]

#  [[ 0.  0.  0.  0.  0.]
#   [ 0.  0.  1.  1.  0.]
#   [ 0.  0.  1.  1.  0.]
#   [ 0.  0.  1.  1.  0.]
#   [ 0.  0.  0.  0.  0.]
#   [ 0.  0.  0.  0.  0.]]]

Answer 2

此功能将在某个轴的末尾填充如果你想填两面，只需修改它。

def pad_along_axis(array: np.ndarray, target_length, axis=0):

    pad_size = target_length - array.shape[axis]
    axis_nb = len(array.shape)

    if pad_size < 0:
        return a

    npad = [(0, 0) for x in range(axis_nb)]
    npad[axis] = (0, pad_size)

    b = np.pad(array, pad_width=npad, mode='constant', constant_values=0)

    return b

示例：

>>> a = np.identity(5)
>>> b = pad_along_axis(a, 7, axis=1)
>>> print(a,a.shape)
[[1. 0. 0. 0. 0.]
 [0. 1. 0. 0. 0.]
 [0. 0. 1. 0. 0.]
 [0. 0. 0. 1. 0.]
 [0. 0. 0. 0. 1.]] (5, 5)

>>> print(b,b.shape)
[[1. 0. 0. 0. 0. 0. 0.]
 [0. 1. 0. 0. 0. 0. 0.]
 [0. 0. 1. 0. 0. 0. 0.]
 [0. 0. 0. 1. 0. 0. 0.]
 [0. 0. 0. 0. 1. 0. 0.]] (5, 7)

如何在某个轴上用零填充张量（Python）

2 个答案: