build a origin destination matrix from 3 vectors without using vec2mat funct

hello everyone, i would know how i can build a origin-destination matrix from 3 vectors: first one is the origin label vector, second the destination label vector and the third one is the distances vector.

A= [[0 0 0;0 1 7;0 2 6;0 3 2;0 4 1;1 0 4;1 1 0;1 2 2;1 3 3;1 4 7;2 0 10;2 1 2;2 2 0;2 3 4;2 4 3;3 0 12;3 1 14;3 2 3;3 3 0;3 4 2;4 0 7;4 1 9;4 2 2;4 3 1;4 4 0]]

for each origin to all destination i have to obtain the corresponding distance value

matrix_dist= [0   7  6  2  1;
4  0  2  3  7;
10  2  0  4  3;
12  14  3  0  2;
7  9  2  1  0]

vec2mat function cannot be used

[Guillaume]

"vec2mat function cannot be used"

Why not? If this is homework, then what effort have you put into this other than posting the question on this forum?

[wardrop89]

vec2mat is able to cut a vector in a determined size to build a full matrix of (nxn) dimension, but if you have some data missing in the OD database the (i,j) position of the element in the matrix suffer a shift. if you have a (3x3) matrix with a missing element, using vec2mat, the answer will be wrong. Given matrix_dist=[ 9 3 2; 4 5 7;11 10 9]

if matrix_dist(1,3) is missing, making use of vec2mat: matrix_dist=vec2mat(matrix_dist,3) produces a irregular solution

matrix_dist =

     9     3     4
     5     7    11
    10     9     0

where (1,3) element induces a global shifting of cutting operation and in (3,3) position the value is wrong and equal to zero

Answer 1

[Guillaume]

I don't really understand your explanation as I don't see how vec2mat would be used for what you want, but given your input the desired output can be simply obtained with:

matrix_dist = zeros(max(A(:, [1 2]))+1);
matrix_dist(sub2ind(size(matrix_dist), A(:, 1)+1, A(:, 2)+1)) = A(:, 3)