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Managing Matrix Content Using Loop ?

Asked by I Made on 24 Mar 2013

e.g i have variable data that containt matrix like these ;

a1 b1 c1

a2 b2 c2

a3 b3 c3

and i wanted it stored like :

a1

a2

a3

b1

b2

b3

c1

c2

c3

I use looping

    inc=1;
    [s1,s2]=size(data);
    for x=1:s2
        for y=1:s1
        dataStored(inc)=data(y,x);
        inc=inc+1;
        end
    end

It's work, but on a very large amount of data like data < 512x3671 int 16 > take endless time to wait. Is there any way simple to do that? Or maybe my code is wrong ?

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1 Answer

Answer by Cedric Wannaz on 24 Mar 2013
Edited by Cedric Wannaz on 24 Mar 2013
Accepted answer
 >> A = magic(3)           % Just an example..
 A =
     8     1     6
     3     5     7
     4     9     2
 >> v = A(:)               % Read A as a column vector (linear indexing).
 v =
     8
     3
     4
     1
     5
     9
     6
     7
     2

6 Comments

Cedric Wannaz on 25 Mar 2013

You can only CAT arrays on dimensions with same length. If you are not in this situation, you have fist to adapt lengths. If b had been a 2x1 vector in the previous case, I would have had to add some padding, e.g. 0, to match lengths:

 >> [a, [b;0]]
 ans =
     6     1
     7     2
     8     0
I Made on 25 Mar 2013

i tried it but get another error : CAT arguments dimensions are not consistent...

which my variable : a < 1879552x1 int16 > and b < 1879402x1 int16 > then i do :

c = [a, [b;0]]

Cedric Wannaz on 25 Mar 2013

Well, [b;0] adds only one 0 element to b and look at the size of each of your vectors.. the size difference is much greater than just one element. It is 150 actually. Now if it is really meaningful to add 150 0's to b, you can do it as follows:

 bext = [b; zeros(150,1)] ;
 c = [a, bext] ;

but as far as I'm concerned, it would be a good investment of your time to read a tutorial, so you understand at least the basics about array manipulation in MATLAB.

Cedric Wannaz

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