How to change 1d array to 2d array under certain conditions

Question

Is there a way through python numpy operations to produce the following result?

Input 1d array :

[3, 0, 0, 2, 2, 1]

Output 2d array :

3 0 0 2 2 1
0 0 0 2 2 1
0 0 0 2 2 1
2 2 2 2 2 1
2 2 2 2 2 1
1 1 1 1 1 1

Answer 1

in addition to jeromie’s brilliant answer, here is a support for unordered array:

indexes = np.arange(len(arr))
idx = np.maximum(indexes[None,:], indexes[:, None])
arr[idx]