Vectorize numpy array expansion

Question

I\'m trying to find a way to vectorize an operation where I take 1 numpy array and expand each element into 4 new points. I\'m currently doing it with Python loop. First l

Answer 1

For the first example, you can do an outer product of the input and the template and reshape the result:

input_array = np.array([1, 2, 3, 4])
template = np.array([0, 1, 1, 0])

np.multiply.outer(input_array, template)
# array([[0, 1, 1, 0],
#        [0, 2, 2, 0],
#        [0, 3, 3, 0],
#        [0, 4, 4, 0]])

result = np.multiply.outer(input_array, template).ravel()
# array([0, 1, 1, 0, 0, 2, 2, 0, 0, 3, 3, 0, 0, 4, 4, 0])

Similarly for your second example you can use np.add.outer

np.add.outer(input_array, [-0.2, -0.2, 0.2, 0.2]).ravel()
# array([ 0.8,  0.8,  1.2,  1.2,  1.8,  1.8,  2.2,  2.2,  2.8,  2.8,  3.2,
        3.2,  3.8,  3.8,  4.2,  4.2])

See:

• http://docs.scipy.org/doc/numpy/reference/generated/numpy.ufunc.outer.html