如何在 python 中用 for 循环填充二维数组的每个元素

Question

Whats happening is the loop is iterating and filling the elements of the array, but 'element wise' - ie it is calculating the first element correctly, then looping again and filling the first element again with what should be the second element....so ultimately, i have a 2d array/matrix filled with the values that should only be in the last element of my matrix. How to make it such that once the first element is filled, the for loop moves on to the next element and the next value?

Heres what Ive tried:

sim_matrix=np.zeros((3,3), dtype=float)

for i in range(0,3):
    for j in range(0,3):
        for k in range(0,3):
            for l in range(0,3):
                    sim_matrix[i][j]=node_list_bsc[0][k]['bsc mean value']-node_list_bsc[1][l]['bsc mean value']

#node_list_bsc[x][y]['bsc mean value'] are float values - they are stored in a list of dictionaries,
#hence the double indexing

this gives:

array([[1.14488261e-08, 1.14488261e-08, 1.14488261e-08],
       [1.14488261e-08, 1.14488261e-08, 1.14488261e-08],
       [1.14488261e-08, 1.14488261e-08, 1.14488261e-08]])

but it should give:

[[-5.131371757023141e-10, -7.509188731093747e-08, 7.67647989217221e-07],
 [8.933230795306053e-08, 1.475355781782538e-08, 8.574934343459839e-07],
 [-7.567123003427902e-07, -8.312910504780254e-07, 1.144882605013307e-08]]

So as you can see, its filling up with the last element only. I ran the print command from within the centre of these nest for loops to see how it was filling, and its like this: (example)

[[-5.13137176e-10  0.00000000e+00  0.00000000e+00]
 [ 0.00000000e+00  0.00000000e+00  0.00000000e+00]
 [ 0.00000000e+00  0.00000000e+00  0.00000000e+00]]

[[-7.50918873e-08  0.00000000e+00  0.00000000e+00]
 [ 0.00000000e+00  0.00000000e+00  0.00000000e+00]
 [ 0.00000000e+00  0.00000000e+00  0.00000000e+00]]...

ie first element is correct but then gets replaced by 2nd element. This is probably obvious already from the code but I think its still useful to illustrate. I've also tried with while loops, and if - else statements - something like:

#pseudo code following:
for i in range(0,3):
    for j in range(0,3):
        for k in range(0,3):
            for l in range(0,3):
            if sim_matrix[i][j]==0.0:
                    sim_matrix[i][j]=node_list_bsc[0][k]['bsc mean value']-node_list_bsc[1][l]['bsc mean value']
            else: continue

It feels pretty close - but i just cant quite figure out where Im going wrong!

Answer 1

As I understand your problem, you are getting the same number in every place of your 2D array. At first, it is difficult to suggest anything without knowing about "node_list_bsc". However, to assign values to a 2D array you only need two loops. Your code can be written as sim_matrix=np.zeros((3,3), dtype=float)

for i in range(0,3):
    for j in range(0,3):
        if sim_matrix[i][j]==0.0:
            sim_matrix[i][j]=node_list_bsc[0][i]['bsc mean value']- node_list_bsc[1][j]['bsc mean value']

If it does not work, let me know and provide more information about node_list_bsc.