在 ndarray 中搜索 one-hot 编码的 label

Question

I have an ndarray called labels with a shape of (6000, 8) . This is 6000 one-hot encoded arrays with 8 categories. I want to search for labels that looks like this:

[1,0,0,0,0,0,0,0]

and then tried to do like this

np.where(labels==[1,0,0,0,0,0,0,0,0])

but this does not produce the expected result

Answer 1

You need all along the second axis:

np.where((labels == [1,0,0,0,0,0,0,0]).all(1))

---

See with this smaller example:

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

(labels == [1,0,0,0,0,0,0,0])

array([[ True,  True,  True, False,  True,  True,  True,  True],
       [False,  True,  True,  True,  True, False, False,  True],
       [ True,  True,  True,  True,  True,  True,  True,  True],
       [False,  True,  True,  True,  True,  True,  True, False]])

Note that the above comparisson simply returns an array of the same shape as labels , since the comparisson has taken place along the rows of labels . You need to aggregate with all , to check whether all elements in a row are True :

(labels == [1,0,0,0,0,0,0,0]).all(1)
 #array([False, False,  True, False])