I'm trying to do a sorting algorithm and I need to do something like this:
arr = numpy.array([2,4,5,6])
#some function here or something
array([5,2,4,6])
#element "5" moved from position 3 to 1, and all of the others moved up one position
What I mean is I want to change an element's position (index) and move all the other elements up one position. Is this possible?
You could use numpy.roll() with a subset assignment:
arr = numpy.array([2,4,5,6])
arr[:3] = numpy.roll(arr[:3],1)
print(arr)
[5 2 4 6]
numpy.roll create a copy of the array or it does it in-place in the same array?
If you know the position/index of the element to be shifted, then you could do:
indx = 2
np.r_[arr[indx], np.delete(arr, indx)]
Out[]: array([5, 2, 4, 6])
You could do this in-place without the need of creating first an intermediate array of n-1 elements and then creating another final array by concatenation. Instead, you could try this:
idx = 2
tmp = arr[idx]
arr[1:idx+1] = arr[0:idx]
arr[0] = tmp
So there are more than one ways of doing this, and the choice depends upon your algorithm's constraints.