Average values for duplicates in (:,1)

Hi, I have written a script with a for loop in it that plots two measurements (water tempurature and salinity) for a given depth and a given x position. There are only 7 different x locations. I have a matix B being produced in a for loop for various depths, a new B for each new depth. Where B=[xdistance,Temp,Sal] e.g

B=
000 14 33
000 14 34
700 13 35
700 13 36
700 12 35 . . .

how can I average B such that there are no duplicates in B(:,1)

B=
000 14 33.5
700 12.67 35.67 ...

without having to specify the length of B as it will change for each depth (each iteration of the for loop).

Answer 1

[Andrei Bobrov]

[A,~,ii] = unique(B(:,1),'stable');
x = B(:,[2,3]);
[a,b] = ndgrid(ii,1:2);
A(:,2:3) = accumarray([a(:),b(:)],x(:))./(accumarray(ii,1)*ones(1,size(x,2)));

Answer 2

[Stephen23]

You can use unique and accumarray very efficiently:

B = [...
000 14 33
000 14 34
700 13 35
700 13 36
700 12 35]

[A,~,z] = unique(B(:,1),'stable');
A(:,2) = accumarray(z,B(:,2),[],@mean);
A(:,3) = accumarray(z,B(:,3),[],@mean);

Generates this output matrix:

>> A
A =
   0.00000    14.00000    33.50000
 700.00000    12.66667    35.33333