# reshape matrix with variable length to vector

4 views (last 30 days)
Houssam on 17 Jun 2021
Commented: Atsushi Ueno on 17 Jun 2021
hi matlab community
i have a matrix with variable length, i want to convert it to a vector like this
matrix = [ 1 2 3; 4 5 6; 7 8 9] to vector = [1 2 3 4 5 6 7 8 9]
i ve tried
reshape(matrix, [1, 9])
but it gives me
1 4 7 2 5 8 3 6 9
PS. i can do it with a for loop but i want to use a single line code
Atsushi Ueno on 17 Jun 2021
This is for understanding the reasonw why.
MATLAB® and Fortran use column-major layout by default.

Stephen Cobeldick on 17 Jun 2021
M = [1,2,3;4,5,6;7,8,9]
M = 3×3
1 2 3 4 5 6 7 8 9
V = reshape(M.',1,[])
V = 1×9
1 2 3 4 5 6 7 8 9

John D'Errico on 17 Jun 2021
Edited: John D'Errico on 17 Jun 2021
Look at the order the elements were returned. Do you know how the elements of a matrix are stored? DOWN THE COLUMNS. So when you reshaped the vector, it gave you the elements of column 1, then column 2, etc.
All you need to do is to TRANSPOSE THE ARRAY, BEFORE the reshape.
reshape(matrix.', [1, 9])
This has the effect of turning columns into rows, and vice versa. And that is what you need.
Understanding how the elements are stored in an array is one of the most important things you can learn as you will go forwards in MATLAB. This will help you to solve many problems.