Calculating the averages of different groups of values

Hi,

I need to get averages of Ys, corresponds to similar groups of Xs separately, without combining the similar groups at two different places. What I mean is, the values of Ys (1,2,4) for the first set of X=3 should not combine with 10 which is Y for X=3 at the end.

Consider two vectors are as follows. Also, it is better if you do not use 'accumarray' command.

x=[3 3 3 4 4 5 5 5 5 3 11]; 
y=[1 2 4 5 7 1 1 8 10 10 1];

Thanks a lot.

Answer 1

[Mohammad Abouali]

x=[3 3 3 4 4 5 5 5 5 3 11]; 
y=[1 2 4 5 7 1 1 8 10 10 1];
groupBounds=[0; find(diff([x(:); NaN])~=0)];
groupAverage=arrayfun(@(gID) mean(y( (groupBounds(gID)+1):(groupBounds(gID+1)) )),1:(numel(groupBounds)-1));

fprintf('grpStartIDX   grpEndIDX   x_new   y_new\n');
fprintf('%11d   %9d   %5d   %5.2f\n',...
        [(groupBounds(1:end-1)+1)'; ... %grpStartIDX
         groupBounds(2:end)'; ... %grpEndIDX
         x(groupBounds(2:end)); ... %x_new
         groupAverage; ... %y_new
         ])

when you run it, you will get:

grpStartIDX   grpEndIDX   x_new   y_new
          1           3       3    2.33
          4           5       4    6.00
          6           9       5    5.00
         10          10       3   10.00
         11          11      11    1.00