Replace all the value except for the one a specified index of a numpy matrix with zero-CodePudding

I have the following array

graph2 = [[0, 10, 15, 20],
        [10, 0, 35, 25],
        [15, 35, 0, 30],
        [20, 25, 30, 0]]

I want to replace all to zero except for values at a specific index. Like Index (1,4), so the 20 at first line i don't place zero (4,3) the 30 at fourth list, and (3,1) the 15 in third list

CodePudding user response：

Remember that list index Starts at 1 not at 0. So your list indexes are wrong. I fixed them below

graph2 = [[0, 10, 15, 20],
        [10, 0, 35, 25],
        [15, 35, 0, 30],
        [20, 25, 30, 0]]
skip = [(0, 3), (3, 2), (2,0)]
for i in range(len(graph2)):
    for j in range(len(graph2[i])):
        if (i, j) in skip:
            continue
        else:
            graph2[i][j] = 0
print(graph2)

This should work

CodePudding user response：

Assuming the indices to skip are few, why not create a new numpy array of zeros and fill the values from the original array like:

newgraph = np.zeros(graph2.shape, dtype=np.int8)
indices = [[0, 3], [3, 2], [2, 0]]
for i, j in indices:
    newgraph[i,j] = graph2[i, j]

print(newgraph):

[[ 0  0  0 20]
 [ 0  0  0  0]
 [15  0  0  0]
 [ 0  0 30  0]]