find sum of all the entries with value 0

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arun
arun 2013-11-29
评论： Jos (10584) 2013-12-2
I have a cell matrix of mat = [ 1 0 0 4;0 2 0 4], i want to find the sum of the all the entries having value 0. in the case of given example the entries having count 0 are 4; so sum will be 4. how can i do this.

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Matt J
Matt J 2013-11-29
编辑：Matt J 2013-11-29
sum(~mat(:))
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Matt J
Matt J 2013-11-29
编辑：Matt J 2013-11-29
No, what I proposed
sum(~mat(:))
works indepedently of ndims(mat) and will save you additional function calls to sum().
arun
arun 2013-11-30
okieee,sorry............... i got it.

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Jos (10584)
Jos (10584) 2013-11-30
NNZ is the dedicated function to do this:
nnz(~mat)
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John D'Errico
John D'Errico 2013-11-30
Note that nnz(~mat) will be poor even for large sparse matrices, because if mat is sparse, then ~mat must create a large and rather dense logical matrix. Better then would be to use a form like:
numel(mat) - nnz(mat)
In my tests, for a large fairly sparse matrix like that generated by Matt in his comment, my form was the fastest.
Jos (10584)
Jos (10584) 2013-12-2
Thanks, Matt and John, for the insights.

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