Summing up subsequent rows if equal

well, I have been trying to sum up the values of the third column if the values of the rows (considering values in the first and second column only) tare equal. But couldnt suceed. It would be of great help if anyone would help me out with it.

A = [ 2 3 5

3 4 5

2 3 5

3 4 5

5 6 6

2 3 5

5 6 6

3 4 5 ];

The code i wrote is as follows

m,n] = size (A);

for i = 1:(m-1)

BB=[];

for j = i+1:(m)

if A(i,1)== A(j,1)

if A(i,2)== A(j,2)

B(i)= A(i, 3)+ A(j,3)

BB(k)=[A(i,1),A(i,2),BB(k)+B(i)]

end

end

end

end

The result I need is as follows

BB= [ 2 3 15

3 4 15

5 6 12 ];

Answer 1

[Dyuman Joshi]

There is another approach you can follow -

A = [  2 3 5 
        3 4 5 
        2 3 5 
        3 4 5 
        5 6 6 
        2 3 5 
        5 6 6 
        3 4 5];

%Get the unique combinations of rows from the first two columns
%and the rows they are in
[B,~,rowidx] = unique(A(:,1:2),'rows')

B = 3×2

2 3 3 4 5 6

rowidx = 8×1

1 2 1 2 3 1 3 2

%Get the sum of values (i.e. 3rd column of A) corresponding to same indices
S = accumarray(rowidx,A(:,3))

S = 3×1

15 15 12

%Final output
Out = [B S]

Out = 3×3

2 3 15 3 4 15 5 6 12

[Stephen23]

+1 yes, that is a good approach.

[neil vaz]

Thank you Dyuman Joshi !!

Answer 2

[Angelo Yeo]

A = [2 3 5
    3 4 5
    2 3 5
    3 4 5
    5 6 6
    2 3 5
    5 6 6
    3 4 5 ];

kindOfRowVec = unique(A(:, 1:2),'rows');
BB = [kindOfRowVec, zeros(size(kindOfRowVec, 1), 1)];
for i_kind = 1:size(kindOfRowVec, 1)
    idx = any(A(:, 1:2) == kindOfRowVec(i_kind, :), 2);
    BB(i_kind, 3) = sum(A(idx, 3));
end
BB

BB = 3×3

2 3 15 3 4 15 5 6 12

[neil vaz]

Thank you Angelo Yeo!!

Answer 3

[Diya Tulshan]

Hii Neil Vaz,

I understand you want to debug the code and get the desired output.

Here's a solution that might help:-

A = [2 3 5;
     3 4 5;
     2 3 5;
     3 4 5;
     5 6 6;
     2 3 5;
     5 6 6;
     3 4 5];

% Extract the first two columns
first_two_cols = A(:, 1:2);

% Get unique combinations of the first two columns
unique_combinations = unique(first_two_cols, 'rows', 'stable');

% Initialize the sumvalues array
sumvalues = zeros(size(unique_combinations, 1), 1);

% Loop through each unique combination
for i = 1:size(unique_combinations, 1)
    % Find the rows that match the current unique combination
    matching_rows = all(first_two_cols == unique_combinations(i, :), 2);
    
    % Sum the corresponding values from the third column
    sumvalues(i) = sum(A(matching_rows, 3));
end

% Combine the unique combinations with the summed values
finalvalue= [unique_combinations, sumvalues];

You will be able to see the desired output in the workspace when you run the above code.

Kindly refer to the link below to get a good overview about the function that i have used:

unique:- https://in.mathworks.com/help/matlab/ref/double.unique.html

Hope it helps!

[neil vaz]

Thank you Diya Tulshan!

Answer 4

[Chunru]

A = [  2 3 5 
        3 4 5 
        2 3 5 
        3 4 5 
        5 6 6 
        2 3 5 
        5 6 6 
        3 4 5 ];
[C, ia, ic] = unique(A(:, 1:2), 'rows');
D = [C zeros(size(C,1), 1)];
for i=1:size(C, 1)
    D(i, 3) = sum(A(ic==i, 3));  
end
D

D = 3×3

2 3 15 3 4 15 5 6 12

[neil vaz]

Thank you Chunru!