Sum specific rows of an array

Hi,

I have an array like:

0.2    2    3
1      3    4
1      4    6
0.8    4    6
2      5    1
1      6    2
0.4    6    2

Now I want to code that MATLAB sums up the values of the 1st column in the rows where the value of the 2nd and 3rd column match.

So the result should look like this below:

0.2    2    3
1      3    4
1.8    4    6
2      5    1
1.4    6    2

I hope someone can help me, thank you!

[Bob Thompson]

"where the value of the 2nd and 3rd column match."

How do the values of the 2nd and 3rd column match in any of these rows?

In general form this should be fairly easy with logic indexing.

[yinki23]

Sorry if I was unspecific.

For example, rows no.3 and no.4 both have 4 and 6 in columns no.2 and no.3. So I want to sum these 2 rows up in column 1 (1+0.8). Same with rows no.6 and no.7.

I hope this helps you understand my question.

[James Tursa]

Are the values in columns 2 and 3 always positive integers?

Answer 1

[Andrei Bobrov]

A = [0.2    2    3
1      3    4
1      4    6
0.8    4    6
2      5    1
1      6    2
0.4    6    2];

[a,~,c] = unique(A(:,2:3),'rows','stable');
out = [accumarray(c,A(:,1)),a];

[yinki23]

Thank you so much! Works perfect for me!

Answer 2

[s]

clc;
clear all;
A = [0.2    2    3;1      3    4;1      4    6;0.8    4    6;2      5    1;1      6    2;0.4    6    2];
B = size (A,1);
Result = [];
n = 0;
for i = 1:1:B-1
    
      if (A(i,2) == A(i+1,2) && A(i,3) == A(i+1,3))
          n = n+1;
      end
     
end

for j = 1:1:B-n
    if (A(j,2) == A(j+1,2) && A(j,3) == A(j+1,3))
        Sum = A(j,1)+A(j+1,1);
        Result = [Result; Sum A(j,2) A(j,3)]
        A([j+1],:) = [];
      else 
         Result = [Result; A(j,1) A(j,2) A(j,3)]
    end
end

This should help