generate sequence by indices / one-hot encoding

Question

I have a sequence s = [4,3,1,0,5] and num_classes = 6 and I want to generate a Numpy matrix m of shape (len(s), num_classes)

Answer 1

You can use broadcasting -

(np.array(s)[:,None]==np.arange(num_classes))+0

Sample run -

In [439]: s
Out[439]: [4, 3, 1, 0, 5]

In [440]: num_classes = 9

In [441]: (np.array(s)[:,None]==np.arange(num_classes))+0
Out[441]: 
array([[0, 0, 0, 0, 1, 0, 0, 0, 0],
       [0, 0, 0, 1, 0, 0, 0, 0, 0],
       [0, 1, 0, 0, 0, 0, 0, 0, 0],
       [1, 0, 0, 0, 0, 0, 0, 0, 0],
       [0, 0, 0, 0, 0, 1, 0, 0, 0]])