How to get row and column from a vector size

Hi matlab Community

i am back again with anouther question

i have a vector with variable length like this :

Vector  = [10    20    30    40    50    60    70    80     9   100]
> numel(Vector) =
    10

or

Vector = [ 1 2 3 4 5 ]
> numel(Vector) =
    5

i want to reshape the vector to a matrix with the 2 largest row and coluumn.

but i can't find out how to go from vector size to matrix row and column

thanks in advance

[SALAH ALRABEEI]

use reshape(A,n,m) where the number of elements in A must = nxm

[James Tursa]

What do you mean by "2 largest row and column"? Please give examples of reshaped results.

[the cyclist]

Also, because 5 is a prime number, your example

Vector = [ 1 2 3 4 5 ];

cannot be shaped into a matrix (other than 1x5 or 5x1), so you might want to clarify that case as well.

Answer 1

[Scott MacKenzie]

Assuming the vector length being a prime number (as noted by @the cyclist) is just one possible case of many, then the following code achieves the desired goal:

% test vector
v = rand(1,randi([1 100]));

n = length(v);
n1 = round(sqrt(n));

while n1 > 1
    if ~rem(n,n1)
        break;
    end
    n1 = n1 - 1;
end
n2 = n/n1;
fprintf('For %d elements, max matrix is %d x %d\n', n, n1, n2);
M = reshape(v, n1, n2); % reshaped vector

Output for some example runs:

For 18 elements, max matrix is 3 x 6

For 36 elements, max matrix is 6 x 6

For 44 elements, max matrix is 4 x 11

For 59 elements, max matrix is 1 x 59

[Houssam]

thanks very mush, this exactly what i was looking for,

but there is always that problem of primary numbers!

so i've decided to to choose 512 as a number of columns

and add zeros at the end of the file so that it can be devided by that number of rows