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Re: Counting problem
Posted:
Feb 7, 2013 9:54 AM


"Jos (10584) " <#10584@fileexchange.com> wrote in message news:kf040a$35i$1@newscl01ah.mathworks.com... > "Erasmus" wrote in message <keuijo$cvu$1@newscl01ah.mathworks.com>... >> hello everyone, I want count how many times of number meet the specific >> criteria. >> for example, I have two matrix, A and B, I want to count the how many >> times of element meet two criteria,1) the element in A is less than 1; 2) >> the corresponding element(in the same location) in B is larger than 50,. >> >> for example >> >> A= [ 0.1 0.2 0.5 >> 0.9 1.3 1.2 0.7 1.2 1.5] >> B=[2 34 43 >> 54 55 56 >> 62 43 45] >> >> so meet the times meeting these two criteria is 2 times, location[3,1] >> and [2,1] >> >> Does anyone can help me? thank you very much! > > Create logical matrices using your criteria, like tfA = A < 1 > tfB = B > 50 > tfAB = tfA & tfB > N = sum(tfAB(:)) > > The colon is needed to sum over all elements. All this can be combined in > a single line, which is, however, more difficult to understand. > > N = sum(A(:)< 1 & B(:)>50)
There's no need for SUM here since you're just looking for a count of the nonzeros.
tfA = A < 1 tfB = B > 50 tfAB = tfA & tfB N = nnz(tfAB)
This leads to the oneliner:
N = nnz( (A < 1) & (B > 50) );
The only part of that statement that IMO may be difficult to understand is the NNZ function, which not a lot of people tend to use or perhaps know about. [NNZ: it's not just for sparse matrices anymore! ;]
 Steve Lord slord@mathworks.com To contact Technical Support use the Contact Us link on http://www.mathworks.com



