Create new array with array elements/amounts set by two other arrays in Python

Question

I have two arrays in Python (numpy arrays):

a=array([5,7,3,5])
b=array([1,2,3,4])

and I wish to create a third array with each element from b appearing a times in the new array, as:

c=array([1,1,1,1,1,2,2,2,2,2,2,2,3,3,3,4,4,4,4,4])

Is there a fast, numPythonic way of doing this with a minimum of looping? I need to use this operation thousands of times in a loop over a fairly large array, so I would like to have it be as fast as possible.

Cheers, Mike

mgibsonbr · Accepted Answer · 2012-02-10 19:09:31Z

5

I believe repeat is what you want:

c = repeat(b, a)

answered Feb 10, 2012 at 19:09

mgibsonbr

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