For loop versus Matrix notation
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Can this be simplified to use a matrix expression instead of a for loop?:
X=[1 5.4; 1 6.3; 2 4.8; 3 7.1];
dates=X(:,1);
amounts=X(:,2);
uniquedates=unique(dates);
totals=zeros(size(uniquedates));
for d = 1:size(uniquedates,1)
totals(d,1)=sum(amounts(dates==uniquedates(d,1)));
end
Y = [uniquedates totals];
2 Comments
Matt Kindig
on 29 Jan 2013
Probably, but likely not in an easy-to-understand way. The fact that totals differs in size from dates complicates things.
Is there a reason you don't want to just use the for-loop?
Accepted Answer
Oleg Komarov
on 30 Jan 2013
Y = [uniquedates accumarray(X(:,1),X(:,2))];
3 Comments
Oleg Komarov
on 30 Jan 2013
Map the dates to a set X in the positive N, i.e. use unique on the dates and then X(:,1) is the ia index from the call to unique.
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