How to use array values as matrix coordinates to insert values in the matrix

Question

I have two arrays x and y of size 4013. The values of x array are row indices and of y array are column indices. I want to create a matrix of size 512*512 and insert values using x and y indices. How can I do this ?

Those x and y would act as the indices, but what values would you put in there in the matrix and what about the indices of the matrix that won't be indexed with them? — Divakar
– Divakar, Commented Apr 19, 2014 at 14:45
I am dealing with an gray scale image(matrix of 512*512). At first i have extracted those pixel locations having value 255(logical 1) using find() function from the image in x and y array. x contains row value of that pixel and y contains column value. Now i want to create a new matrix and put 255(logical 1) value in the row and column location of x and y, other location values will be 0. — user3162506
– user3162506, Commented Apr 20, 2014 at 9:48
I missed this comment about the 255 value earlier. Edited the answer now. — buzjwa
– buzjwa, Commented Apr 22, 2014 at 11:09

buzjwa · Accepted Answer · 2014-04-22 11:09:23Z

2

You can use sub2ind to turn index vectors into matrix indices. For example:

x = randi(512, 4000, 1);
y = randi(512, 4000, 1);
val = 255;
mat = zeros(512, 512);
mat(sub2ind(size(mat), y, x)) = val;

edited Apr 22, 2014 at 11:09

answered Apr 19, 2014 at 15:05

buzjwa

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