MATLAB: Sum elements in a column where there are matching values in an adjacent column

average if element equal to another in same columnsum if column matches

I have a numeric matrix A = [1 1 100; 1 2 200; 1 3 50; 2 1 100; 2 2 200; 2 3 50; 3 1 100; 3 2 200; 3 3 50; 3 4 20]
I am trying to obtain a vector of values of equal dimension e.g. ans = [0; 0; 0; 100; 200; 50; 200; 400; 100; 0]
My aim is to sum & average prior elements in the 3rd column where the corresponding element in the 2nd column value matches, not including the row each vector element corresponds to. I hope I have made this question clear, but please don't hesitate to ask for clarification if not. I have lots of rows to process hence a time efficient solution would be greatly appreciated.
Note: I have tried my best to find a solution from scanning through the previous Q & As but haven't had any luck so far.

Best Answer

Here's one way, there are probably better ones, but this works:
NEW
A = [1 1 100; 1 2 200; 1 3 50; 2 1 100; 2 2 200; 2 3 50; 3 1 100; 3 2 200; 3 3 50; 3 4 20];
[~,~,idx] = unique(A(:,2)); % Unique second column indices

A3 = A(:,3); % third column values

% Build array with index and cumulative value

idxdv = accumarray(idx,(1:numel(idx))',[],@(x){[sort(x) cumsum(A3(sort(x)))]});
idxdv = cell2mat(cellfun(@(x)[x(:,1), [0;x(1:end-1,2)]],idxdv,'UniformOutput',false))
% Sort it by index and extract second column

dv = sortrows(idxdv);
results = dv(:,2)
OLD, for reference in comments
A = [1 1 100; 1 2 200; 1 3 50; 2 1 100; 2 2 200; 2 3 50; 3 1 100; 3 2 200; 3 3 50; 3 4 20];
[~,~,idx] = unique(A(:,2)); % Unique second column indices
A3 = A(:,3); % third column values
% Build array with index and cumulative value
idxdv = cell2mat(accumarray(idx,(1:numel(idx))',[],@(x){[sort(x) cumsum([0;A3(sort(x(1:end-1)))])]}));
% Sort it by index and extract second column
dv = sortrows(idxdv);
results = dv(:,2)
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