I have the following numpy array a = np.array([1,1,2,1,3]) that should be transformed into the following array b = np.array([1,1,1,1,1,1,1,1]).
What happens is that all the non 1 values in the a array should be expanded in the b array to their multiple defined in the a array. Simpler said, the 2 should become 2 ones, and the 3 should become 3 ones.
Frankly, I couldn't find a numpy function that does this, but I'm sure one exists. Any advice would be very welcome! Thank you!
We can simply do -
np.ones(a.sum(),dtype=int)
This will accomodate all numbers : 1s and non-1s, because of the summing and hence give us the desired output.
In [71]: np.ones(len(a),int).repeat(a)
Out[71]: array([1, 1, 1, 1, 1, 1, 1, 1])
For this small example it is faster than np.ones(a.sum(),int), but it doesn't scale quite as well. But overall both are fast.
Here's one possible way based on the number you wanna be repeated:
In [12]: a = np.array([1,1,2,1,3])
In [13]: mask = a != 1
In [14]: np.concatenate((a[~mask], np.repeat(1, np.prod(a[mask]))))
Out[14]: array([1, 1, 1, 1, 1, 1, 1, 1, 1])
