Is it possible to vectorize the insertion of rows?
I have a large 2D numpy array arr (below) and a list of indices. For each index of arr in indices I would like to insert the row at that index back into arr row 5 times at that same index.
indices = [2, 4, 5, 9, 11, 12, 16, 18, 19]
Currently I'm just looping through all the indices and inserting new rows. This approach is slow for a large list of thousands of rows, so for performance reasons I'm wondering is it possible to vectorize this multi-point tile-type insertion?
arr = [
[' ', ' ', 'd'],
[' ', 'd', ' '],
[' ', 'd', 'd'], # <-- reinsert arr[2] here 5 times
['d', ' ', ' '],
['d', ' ', 'd'], # <-- reinsert arr[4] here 5 times
['d', 'd', ' '], # <-- reinsert arr[5] here 5 times
['d', 'd', 'd'],
[' ', ' ', 'e'],
[' ', 'e', ' '],
[' ', 'e', 'e'], # <-- reinsert arr[9] here 5 times
['e', ' ', ' '],
['e', ' ', 'e'], # <-- reinsert arr[11] here 5 times
['e', 'e', ' '], # <-- reinsert arr[12] here 5 times
['e', 'e', 'e'],
[' ', ' ', 'f'],
[' ', 'f', ' '],
[' ', 'f', 'f'], # <-- reinsert arr[16] here 5 times
['f', ' ', ' '],
['f', ' ', 'f'], # <-- reinsert arr[18] here 5 times
['f', 'f', ' '] # <-- reinsert arr[19] here 5 times
]
Example of first insertion of desired result:
arr = [
[' ', ' ', 'd'],
[' ', 'd', ' '],
[' ', 'd', 'd'], # <-- arr[2]
[' ', 'd', 'd'], # <-- new insert
[' ', 'd', 'd'], # <-- new insert
[' ', 'd', 'd'], # <-- new insert
[' ', 'd', 'd'], # <-- new insert
[' ', 'd', 'd'], # <-- new insert
['d', ' ', ' ']
#...
]
You could use np.repeat for this:
indices = [2, 4, 5, 9, 11, 12, 16, 18, 19]
rpt = np.ones(len(arr), dtype=int)
rpt[indices] = 5
np.repeat(arr, rpt, axis=0)