Matrix manipulation from one to another one

How to generate

A= [ 1  0  3  0   0; ...
     0  7  0  0  10; ...
     0  0  0  14 15]

from

 B = [1 2 3 4 5; ...
      6 7 8 9 10; ...
      11 12 13 14 15]

[EDITED, Jan, Code formatted]

[Akira Agata]

What is the rule to determine whether keeping the number (e.g 1 -> 1) or changing to zero (e.g 2 -> 0) ?

[Prabha Kumaresan]

A needs to get generated in a random manner such that numbers in B should exist in A in any column whereas the rest of the numbers in the same column should be as zero

[Jan]

@Prabha Kumaresan: Did you see, that your complete code appeared in one single line? Then the readers do not have any chance to see, that you are talking about matrices, because it looked like a vector.

I've selected your code with the mouse and hit the "{} Code" button. In addition I've inserted "; ..." for clarity. Please format the code by your own in future questions. And read your question after posting it to fix details, which cannot be understood by the readers. Thanks.

Answer 1

[Akira Agata]

Here is the B = [multiple rows * multiple columns] example.

B = reshape(1:64,8,8); % Create 8x8 sample matrix
idx = rand(size(B)) > 0.5; % Randomly select whether keep it or change to zero
A = B;
A(idx) = 0;

[Prabha Kumaresan]

but i want to have only one number in each column rest of the other place where the number holds should be 0.

[Akira Agata]

OK. Then, how about the following code?

B = [1 2 3 4 5; ...
  6 7 8 9 10; ...
  11 12 13 14 15];

sz = size(B);

rowPos = randi(sz(1),sz(2),1);
linInd = sub2ind(sz, rowPos, (1:sz(2))');
idx = false(sz);
idx(linInd) = true;

A = B;
A(~idx) = 0;

The output is:

>> A
A =
   1     0     0     4     0
   0     0     8     0     0
   0    12     0     0    15

[Prabha Kumaresan]

thanks for your code.

[Prabha Kumaresan]

How can i plot the graph of A = 1 0 0 4 0; 0 0 8 0 0; 0 12 0 0 15; could u help me?

[Stephen23]

@Prabha Kumaresan: please format your code correct so that it is readable. Jan Simon has already explained how you can do this.

Answer 2

[Jan]

B   = [1 2 3 4 5; ...
       6 7 8 9 10; ...
       11 12 13 14 15];

siz    = size(B);
idx    = sub2ind(siz, randi([1,3], 1, siz(2)), 1:siz(2));
A      = zeros(siz);
A(idx) = B(idx)

[Prabha Kumaresan]

thanks for your response but i am getting error in idx = sub2ind(siz, randi([1,3], 1, siz(2)), 1:siz(2)); stating (Expression or statement is incorrect--possibly unbalanced (, {, or [.).how to overcome it.

[Andrei Bobrov]

Prabha!

All work on my desktop:

>> B   = [1 2 3 4 5; ...
       6 7 8 9 10; ...
       11 12 13 14 15];

siz    = size(B);
idx    = sub2ind(siz, randi([1,3], 1, siz(2)), 1:siz(2));
A      = zeros(siz);
A(idx) = B(idx)

A =
     1     0     3     0     5
     0     0     0     9     0
     0    12     0     0     0
>>

[Andrei Bobrov]

Hi Jan!

+1.

[Jan]

@Prabha: I do not get an error if I run the posted code or the snippet "idx = sub2ind(siz, randi([1,3], 1, siz(2)), 1:siz(2));".

[Prabha Kumaresan]

Thanks for your response.Now the code is getting executed.

Answer 3

[Andrei Bobrov]

A = B;
s = size(A);
[~,ii] = sort(rand(s));
n = s(1)*(0:s(2)-1);
ii = bsxfun(@plus,ii,s(1)*(0:s(2)-1));
jj = zeros(s);
jj(bszfun(@plus,randi([2,s(1)],1,s(2)),n)) = 1;
ii(cumsum(jj)>0) = 0;
A(ii(ii>0)) = 0;

or

A = B;
s = size(A);
A(rand(s) < .5) = 0;
k = ~any(A);
if any(k)
    ii = find(k);
    jj = sub2ind(s,randi(s(1),1,numel(ii)),ii);
    A(jj) = B(jj);
end

[Prabha Kumaresan]

A = B; s = size(A); [~,ii] = sort(rand(s)); n = s(1)*(0:s(2)-1); ii = ii + s(1)*(0:s(2)-1); jj = zeros(s); jj(randi([2,s(1)],1,s(2)) + n) = 1; ii(cumsum(jj)>0) = 0; A(ii(ii>0)) = 0;

If i runthis code i am getting error in this line ii = ii + s(1)*(0:s(2)-1){Error using + Matrix dimensions must agree}.Could you tell me to get rid of it.

[Andrei Bobrov]

I'm corrected.

Use second variant (after word "or").

[Prabha Kumaresan]

If i use the first variant i am unable to get one value in each column with the rest of the other values as zeros.

If i use second variant I am unable to get the result and in the command line L(rand(s) < .5) = 0 what is the pupose of .5 in that command.could you tell me how can i solve it.

[Andrei Bobrov]

Hm! :)

s = size(B);
A = B;
[~,ii] = sort(rand(s));
A(sub2ind(s,ii(1:end-1,:),repmat(1:s(2),s(1)-1,1))) = 0;

[Prabha Kumaresan]

thanks for sending the code.the code is getting executed.

[Prabha Kumaresan]

how can i plot the graph of A with respect to rows and columns for the final output.