Quick way to sum array elements based on flag in another array?
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Say I have 2 arrays: one with "clean" data, and one that tells me which data gets lost, as indicated by zeros. If an element is lost, it should be added to the next observed element. Anybody got a quick one-or-two-liner to come up with the summed array?
Example:
clean = [1 2 3 4 5 6]
lost = [1 0 3 0 0 6]
desired = [1 5 15]
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Accepted Answer
Stephen23
on 14 Jul 2015
Edited: Stephen23
on 14 Jul 2015
Try this:
tmp = (1:numel(lost))-[0,cumsum(lost(1:end-1)==0)];
desired = accumarray(tmp.',clean).'
Tested:
>> clean = [1 2 3 4 5 6];
>> lost = [1 0 3 0 0 6];
>> tmp = (1:numel(lost))-[0,cumsum(lost(1:end-1)==0)];
>> desired = accumarray(tmp.',clean).'
desired =
1 5 15
>> clean = [40 10 50 30 40 10 50 30 40 10 50 30];
>> lost = [40 0 50 30 0 10 0 0 40 10 50 30];
>> tmp = (1:numel(lost))-[0,cumsum(lost(1:end-1)==0)];
>> desired = accumarray(tmp.',clean).'
desired =
40 60 30 50 120 10 50 30
More Answers (2)
Andrei Bobrov
on 14 Jul 2015
Edited: Andrei Bobrov
on 14 Jul 2015
desired = flip(accumarray(cumsum(lost(end:-1:1)~=0)',clean(end:-1:1)),1)';
or
desired = accumarray(cumsum(xor([0,diff(lost > 0)],lost))',clean)';
Sean de Wolski
on 14 Jul 2015
accumarray(interp1(find(lost),1:nnz(lost),1:numel(lost),'next')',clean)
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