在numpy数组中获取特定值的索引

Question

我有以下numpy数组：

arr = [0,0,0,1,0,0,0,0,0,0,0,1,0,1,0,1,0,0,0,0,0,0,0,0,0,0,1]

以下是我如何获取数组中所有0的索引：

inds = []
for index,item in enumerate(arr):     
    if item == 0:
        inds.append(index)

有没有一个numpy函数可以做同样的事情？

- user308827

---

arr = np.array([0,0,0,1,0,0,0,0,0,0,0,1,0,1,0,1,0,0,0,0,0,0,0,0,0,0,1]) 转换为数组以便清晰明了，然后使用以下方法之一：

np.where(arr==0) (array([ 0, 1, 2, 4, 5, ..., 21, 22, 23, 24, 25]),) 切片 where [0] 只获取索引。

- user1121588

你需要的是numpy.argwhere吗？类似于numpy.argwhere(arr == 0)这样的东西。 - chappers

Answer 1

您可以使用@chappers在评论中提到的numpy.argwhere。

arr = np.array([0,0,0,1,0,0,0,0,0,0,0,1,0,1,0,1,0,0,0,0,0,0,0,0,0,0,1])

In [34]: np.argwhere(arr == 0).flatten()
Out[34]:
array([ 0,  1,  2,  4,  5,  6,  7,  8,  9, 10, 12, 14, 16, 17, 18, 19, 20,
       21, 22, 23, 24, 25], dtype=int32)

或者使用 astype(bool) 的反函数：

In [63]: (~arr.astype(bool)).nonzero()[0]
Out[63]:
array([ 0,  1,  2,  4,  5,  6,  7,  8,  9, 10, 12, 14, 16, 17, 18, 19, 20,
       21, 22, 23, 24, 25], dtype=int32)

- Anton Protopopov

Answer 2

>>> arr = np.array([0,0,0,1,0,0,0,0,0,0,0,1,0,1,0,1,0,0,0,0,0,0,0,0,0,0,1])
>>> (arr==0).nonzero()[0]
array([ 0,  1,  2,  4,  5,  6,  7,  8,  9, 10, 12, 14, 16, 17, 18, 19, 20,
       21, 22, 23, 24, 25])

- John La Rooy

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谢谢@John，nonzero末尾的[0]是什么意思？ - user308827

nonzero函数返回一个由数组组成的元组，对应于arr的每个维度。你的数组只有一个维度，但是你仍然需要在那里加入[0]来将它从元组中取出。 - John La Rooy