Measure Sum of column if statements are true

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Panayiotis Christodoulou
评论： Panayiotis Christodoulou 2016-5-31
Hi there,
I have a matrix array of 4 columns
first: ID
Second: ShopID
Third: Visits
Forth: 1 or -1
How can I measure the sum of Visits (3rd column) for every ID (1st column) when the 4th column is 1 and how many visits when the 4th column is -1
Thanks

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采纳的回答

Ahmed Rashid
Ahmed Rashid 2016-5-30
a = [1 1 2 1; 2 2 3 1; 1 1 2 -1; 2 2 1 -1; 3 3 2 1; 1 2 3 1; 1 2 1 -1];
uniqueIds = unique(a(:, 1));
nrOfUniqueIds = length(uniqueIds);
sortedSumOnes = zeros(nrOfUniqueIds, 2); % first column is id second is the sum
sortedSumMinusOnes = zeros(nrOfUniqueIds, 2); % first column is id, second is the sum
for ii = 1:nrOfUniqueIds
sortedSumOnes(ii, :) = [uniqueIds(ii), sum(a((a(:, 4) == 1) & (a(:, 1) == uniqueIds(ii)), 3))];
sortedSumMinusOnes(ii, :) = [uniqueIds(ii), sum(a((a(:, 4) == -1) & (a(:, 1) == uniqueIds(ii)), 3))];
end
Just replace the a matrix with your own matrix

更多回答（1 个）

Matt Kindig
Matt Kindig 2016-5-30
There are a couple of ways to do this, but I think the easiest is to use the consolidator function on the File Exchange here:
In that way, the result would be found as
% suppose "M" is your N x 4 matrix
positive = (M(:,4)==1);
negative = (M(:,4)==-1);
[ID, positiveSum] = consolidator(M(positive,1), M(positive,3), @sum);
[ID, negativeSum] = consolidator(M(negative,1), M(negative,3), @sum);

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