Repeat each value of an array two times (numpy)

Question

Let A be a numpy array like :

A = np.array([1, 2, 3, 4, 5])

I want to find the cleaner way to produce a new array with each v

Answer 1

If you need to do this operation in a time critical region, the following code is the fastest (using Numpy 1.9 development version):

In [1]: A = numpy.array([1, 2, 3, 4, 5]*1000) 
In [2]: %timeit numpy.array([A, A]).T.ravel('F')
100000 loops, best of 3: 6.44 µs per loop

Note that flatten would make an additional copy, so ravel should be used instead.

If you prefer readability, the column_stack and repeat functions are better:

In [3]: %timeit numpy.column_stack((A, A)).ravel()
100000 loops, best of 3: 15.4 µs per loop

In [4]: timeit numpy.repeat(A, 2)
10000 loops, best of 3: 53.9 µs per loop