James Atwood James Atwood - 2 months ago 27
Python Question

Numpy 1-hot array

Let's say I have a 1d numpy array

a=[1,0,3]


I would like to encode this as a 2d 1-hot array

b=[[0,1,0,0], [1,0,0,0], [0,0,0,1]]


Is there a quick way to do this? Quicker than just looping over a to set elements of b, that is.

YXD YXD
Answer

Your array a defines the columns, you just need to define the rows and then use fancy indexing:

>>> a = np.array([1, 0, 3])
>>> b = np.zeros((3, 4))
>>> b[np.arange(3), a] = 1
>>> b
array([[ 0.,  1.,  0.,  0.],
       [ 1.,  0.,  0.,  0.],
       [ 0.,  0.,  0.,  1.]])
>>>

This is just for illustration. You may want to choose a more appropriate dtype for b such as np.bool.

Comments