I want to combine two or more row with same first column in the matrix .

Salam: I want to combine two or more row with same first column in the matrix .

from

A = [1 2 3 4;
     1 5 6 1;
     2 2 3 4;
     2 5 6 1;
     2 6 7 8;
     3 1 2 3;
     4 1 2 3 
     4 5 8 7];

to

      A = [1 2 3 4 5 6 1 0 0 0;
           2 2 3 4 5 6 1 6 7 8;
           3 6 7 8 0 0 0 0 0 0;
           4 1 2 3 5 8 7 0 0 0];

[Jan]

The 3rd line of the output should be:

3 1 2 3 0 0 0 ..

instead of

3 6 7 8 0 0 0 ...

Answer 1

[Jan]

A = [1 2 3 4;
     1 5 6 1;
     2 2 3 4;
     2 5 6 1;
     2 6 7 8;
     3 1 2 3;
     4 1 2 3 
     4 5 8 7];

key = A(:, 1);
v   = unique(key);
B(:, 1) = v;
for index = 1:length(v)
  data = A(key == v(index), 2:end).';
  B(index, 2:numel(data) + 1) = reshape(data, 1, []);
end

Answer 2

[Geoff Hayes]

zainab - there are several ways to solve this problem. You can use unique to get the unique integers in the first column of A as

 uniqueColumn1Values = unique(A(:,1));

then you can iterate over each of these unique values and find all of those rows which start with that unique value. First, size your output matrix B using mode to determine what is the maximum number of columns for B (we use mode to return the most frequent value in the first column of A and use the frequency f to determine that maximum)

 [m,f] = mode(A(:,1));
 B     = zeros(length(uniqueColumn1Values),f*(size(A,2)-1)+1);
 B(:,1) = uniqueColumn1Values;

 for k=1:length(uniqueColumn1Values)
     idcs = find(A(:,1)==uniqueColumn1Values(k));        % get indices of matching rows
     temp = A(idcs,2:end);                               % create temp matrix
     B(k,2:numel(temp)+1) = reshape(temp',1,numel(temp));  % reshape matrix to array
 end

The above sets B as

 B =

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

There is a lot going on in the above code so you may want to step through it with the debugger to get a better idea as to what is going on.

I do suspect that there are easier ways to get the above too! :)

Answer 3

[Matt J]

S=accumarray(A(:,1),(1:size(A,1)).',[],@(r) {reshape(A(r,2:end),1,[])});

   N=max(cellfun('length',S));
   S=cellfun(@(c)[c,zeros(1,N-length(c))],S,'uni',0);

Anew=vertcat(S{:})