How can I change the 1_D array to the 2_D in specific case?

Hello everyone pleas How can I rewrite the 1_D array(X) into 2_D array(New_X)?

For example:

X=[0 1 0 2 3 0 4 5 6 0 7 8 9 10 0];
into 
New_X(i,j)=[0 1 2 4 7
            1 0 3 5 8
            2 3 0 6 9
            4 5 6 0 10
           7 8 9 10 0];

[Walter Roberson]

What is the logic for skipping values?

Answer 1

[DGM]

It would probably be easier to build the array without starting from the vector, but I imagine it's a requirement. It could be done simply enough with a loop, but I don't feel like loops at the moment.

X=[0 1 0 2 3 0 4 5 6 0 7 8 9 10 0];

n = sqrt(2*numel(X) + 1/4) - 1/2; % find output array size
C = mat2cell(X,1,1:n); % split the vector into chunks
f = @(x) [x zeros(1,n-numel(x))]; % pad chunks to equal length
C = cell2mat(cellfun(f,C,'uniformoutput',false).'); % rearrange
C = C + C.' % combine 

C = 5×5

0 1 2 4 7 1 0 3 5 8 2 3 0 6 9 4 5 6 0 10 7 8 9 10 0

[ahmed noori]

That was amazing thank you so much. i did it with two for loops and counter but the results was incorrect.

[ahmed noori]

We can allso useing (find function) to find output array size, such as :

n=numel(find(X==0));%find output array size

[DGM]

Actually, yeah that works too so long as the diagonal is a unique constant value.

In the case where there are other zeros in the pattern, or if the diagonal is not zero-valued, my method for finding the array size still works (so long as X represents the same triangular portion of the matrix). However, the latter case has an extra complication in assembling the final output. Consider:

% diagonal elements are random or unknown nonzero pattern
X = [-8 1 4 2 3 -1 4 5 6 15 7 8 9 10 -20];

% all this is the same
n = sqrt(2*numel(X) + 1/4) - 1/2;
C = mat2cell(X,1,1:n);
f = @(x) [x zeros(1,n-numel(x))];
C = cell2mat(cellfun(f,C,'uniformoutput',false).');

% but this modification keeps from doubling the diagonal
% this isn't necessary if the diagonal is zero, 
% but it would still work if it were.
C = tril(C,-1) + C.'

C = 5×5

-8 1 2 4 7 1 4 3 5 8 2 3 -1 6 9 4 5 6 15 10 7 8 9 10 -20

[ahmed noori]

Very good example, you explained it very well.