Can you help me ?

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];

[Image Analyst]

Why?

What kind of array do you want? A double with NaN in the "missing" columns on the right, or a cell array with nulls in the missing cells on the right?

[zainab hp]

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];

Answer 1

[Walter Roberson]

Numeric arrays cannot have different number of columns for each row.

[zainab hp]

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];

[Walter Roberson]

A1 = A(:,1);
[uA1, ~, idx] = unique(A1);
maxidx = max(idx);
maxmerge = max( histc(idx, 1:maxidx) );
Anew = zeros(maxidx, size(A,2)*(maxmerge - 1) + 1);
Anew(:,1) = uA1;
for K = 1 : length(idx)
  targetrow = idx(K);

    now put A(K,2:end) at the "end" of Anew(targetrow,:)
  end

Now to put A(K,2:end) at the "end" of Anew(targetrow,:) is left as an exercise for you.

Note: you did not define the order of the row results when column 1 of A is not in sorted order. I picked an arbitrary order that aesthetically pleased me.

Note: you did not define the order of merging the rows that have the same column 1. I picked an arbitrary order that aesthetically pleased me.