将一个 numpy 数组的值添加到特定索引处的 2D numpy 数组的最快方法

Question

I have a 2D numpy array of zeros, a list of numpy arrays (which can be of different lengths) and a list of indices. I want to add the contents of each of the arrays in the list from the start of the corresponding row indice in the 2D array.

Of course, I can just loop over the arrays. However, I need to perform this operations for many different samples. Therefore, I was wondering whether anybody is aware of a more efficient way to do this.

In [1]: A = np.zeros((5, 5))
   ...: arrays = [np.random.randint(1, 10, size=(1,5)) for i in range(3)]
   ...: indices = [1, 3, 4]
   ...: print(arrays)
Out[1]:
[array([3, 1, 3, 6]), array([4, 9]), array([5, 9, 6])]

Expected output:

array([[0., 0., 0., 0., 0.], 
       [3., 1., 3., 6., 0.], 
       [0., 0., 0., 0., 0.], 
       [4., 9., 0., 0., 0.], 
       [5., 9., 6., 0., 0.]] 

Any help would be much appreciated!

Answer 1

Using zip :

for i, a in zip(indices, arrays):
    A[i, :len(a)] = a

Output:

array([[0., 0., 0., 0., 0.],
       [3., 1., 3., 6., 0.],
       [0., 0., 0., 0., 0.],
       [4., 9., 0., 0., 0.],
       [5., 9., 6., 0., 0.]])