How to find the rows with the same values, and to merge those?

I would want to know a way to find the rows having the same value in the first column (id), and combine those rows together.

Suppose I have the matrix A;

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

What I want to do is to find the rows with same ids (1st column), and merge their features (other columns). In this case, I need the following matrix.

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

Answer 1

[Image Analyst]

Sounds like a homework assignment (tag it as homework if that's true), so how about I just get it started for you:

A = [1 2 3 4;
     1 5 6 0;
     2 2 3 4;
     2 5 6 0;
     2 6 7 8;
     3 1 2 3;
     4 1 2 3]
 % Find unique numbers in the first column.
 uniqueCol1 = unique(A(:,1))
 % Find out how many times each number occurs.
 counts = hist(A(:,1), uniqueCol1)
 % Find out how big our output matrix needs to be, and create it.
 rows = length(uniqueCol1);
 columns = 3 * max(counts);
 outputA = zeros(rows, columns, 'int32');
 % Assign first column
 outputA(:,1) = uniqueCol1

You can finish it.

[Sam]

Actually, it is not a homework. I have C background, and just try to learn how to do such things in MATLAB without using for loops .

Thanks

[Image Analyst]

OK. Here's the full script.

workspace
A = [1 2 3 4;
  1 5 6 0;
  2 2 3 4;
  2 5 6 0;
  2 6 7 8;
  3 1 2 3;
  4 1 2 3]
% Find unique numbers in the first column.
uniqueCol1 = unique(A(:,1))
% Find out how many times each number occurs.
counts = hist(A(:,1), uniqueCol1)
% Find out how big our output matrix needs to be, and create it.
rows = length(uniqueCol1);
columns = 3 * max(counts);
outputA = zeros(rows, columns, 'int32');
% Assign first column
outputA(:,1) = uniqueCol1
cols234 = A(:,2:end)
% Fill up output rows.
for row = 1 : length(uniqueCol1)
  % Get a unique number from column 1 of A
  thisNumber = uniqueCol1(row);
  rowsWithThisNumber = A(:,1) == thisNumber; % Logical vector.
  theseRows = cols234(rowsWithThisNumber,:)'; % Row vector
  % Assign this row vector to the row from col 2 onwards.
  outputA(row,2:numel(theseRows)+1) = theseRows(:);
end
% Print to command window.
outputA

Someone may come along with a shorter cryptic one-liner but I think this is easy to understand. If it meets your needs, mark the Answer as accepted.