Store a matrix by columns instead of rows

user_12248827 0
Viewed 45

If I'm given the matrix:

A B C

D E F

G H I

and it is stored in a vector by rows:

[A, B, C, D, E, F, G, H, I]

How can I use the above vector with a for loop to store the transposed version in another vector.

[A, D, G, B, E, H, C, F, I]

vector matrix c++
1 Answers

You have 3 rows with 3 elements (because number of columns is 3) in the old vector and you will have 3 columns with 3 elements (because number of rows is 3) in the new vector.

Therefore, it can be realized like this:

int nRows = 3, nCols = 3;
for (int i = 0; i < nRows * nCols; i++) {
    int r = i / nCols, c = i % nCols;
    new[c * nRows + r] = old[r * nCols + c];
}
user_40623540
Related