零填充numpy数组 [英] Zero pad numpy array

问题描述

在数组末尾加零的更Python方式是什么?

What's the more pythonic way to pad an array with zeros at the end?

def pad(A, length):
    ...

A = np.array([1,2,3,4,5])
pad(A, 8)    # expected : [1,2,3,4,5,0,0,0]

---

在我的实际用例中，实际上我想将数组填充到1024的最接近倍数.例如:1342 => 2048，3000 => 3072

---

In my real use case, in fact I want to pad an array to the closest multiple of 1024. Ex: 1342 => 2048, 3000 => 3072

推荐答案

numpy.pad可以满足您的需要，我们可以在其中传递一个元组作为第二个参数，以告诉每个大小要填充多少个零，例如，(2, 3)将在左侧填充 2 零，在右侧填充 3 零:

numpy.pad with constant mode does what you need, where we can pass a tuple as second argument to tell how many zeros to pad on each size, a (2, 3) for instance will pad 2 zeros on the left side and 3 zeros on the right side:

将A指定为:

A = np.array([1,2,3,4,5])

np.pad(A, (2, 3), 'constant')
# array([0, 0, 1, 2, 3, 4, 5, 0, 0, 0])

还可以通过将元组的元组作为填充宽度来填充2D numpy数组，格式为((top, bottom), (left, right)):

It's also possible to pad a 2D numpy arrays by passing a tuple of tuples as padding width, which takes the format of ((top, bottom), (left, right)):

A = np.array([[1,2],[3,4]])

np.pad(A, ((1,2),(2,1)), 'constant')

#array([[0, 0, 0, 0, 0],           # 1 zero padded to the top
#       [0, 0, 1, 2, 0],           # 2 zeros padded to the bottom
#       [0, 0, 3, 4, 0],           # 2 zeros padded to the left
#       [0, 0, 0, 0, 0],           # 1 zero padded to the right
#       [0, 0, 0, 0, 0]])

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对于您的情况，您可以指定左侧为零，而右侧垫板则根据模块化除法计算得出:

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For your case, you specify the left side to be zero and right side pad calculated from a modular division:

B = np.pad(A, (0, 1024 - len(A)%1024), 'constant')
B
# array([1, 2, 3, ..., 0, 0, 0])
len(B)
# 1024

对于更大的A:

A = np.ones(3000)
B = np.pad(A, (0, 1024 - len(A)%1024), 'constant')
B
# array([ 1.,  1.,  1., ...,  0.,  0.,  0.])

len(B)
# 3072

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