Matrix number of rows reduction to a smaller number of rows.

I have a matrix for example Nrow, by 6 let us say. The first column has numbers 1 thru n which is less than Nrow.. so some rows have same number in column 1. for example the number 3 may be occurring three times and number 4, 4 times etc. I have to reduce the matrix rows from Nrow to n... the rows which have same column 1 number have to be replace by one row which is is a mean of all rows with same number. for e.g. row with column number 3 could be like this

3, 1, 1, 2, 4, 5, 6  
3, 4, 5, 6, 2, 5, 6 
3, 2, 3, 5, 6, 3, 7

so we have three rows with same column 1 that is 3. so I replace these three rows with one row; 3, mean of all three rows. So basically i squeeze the Matrix of [Nrow, 6] to a matrix of [n, 6]; How do I do this?

Thanks in advance.

[Majid Farzaneh]

Hi. I'm not completely sure about my understanding. Is this a correct example for your problem???

Input=

       3     1     1     2     4     5     6
       3     4     5     6     2     5     6
       3     2     3     5     6     3     7

Output     =

3   2.3333    3.0000    4.3333    4.0000    4.3333    6.3333

Which 2.3333 is mean of 1,4,2 (column 2) and 3.000 is mean of 1,5,3 (column 3) etc.

[Pappu Murthy]

that is correct. the three rows now reduce to just one row with column 1 entry being now 3.

Answer 1

[Majid Farzaneh]

Use this:

 % A is your input matrix and B is squeezed matrix
  for i=1:n
    idx=find(i==A(:,1));
    B(i,:)=mean(A(idx,:),1);
  end

[Pappu Murthy]

That worked like charm. Thanks.

[Majid Farzaneh]

:)) You're welcome.