Construct two dimensional numpy array from indices and values of a one dimensional array

Question

Say I\'ve got

Y = np.array([2, 0, 1, 1])

From this I want to obtain a matrix X with shape (len(Y), 3). In this particular cas

Answer 1

To give a one-liner alternative to DSM's perfectly good answer:

>>> Y = np.array([2, 0, 1, 1])
>>> np.arange(3) == Y[:, np.newaxis]
array([[False, False,  True],
       [ True, False, False],
       [False,  True, False],
       [False,  True, False]], dtype=bool)