MATLAB: Quick way to sum array elements based on flag in another array

arrayindexing

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]

Best Answer

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
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