counting strings in cell array, is there a faster solution

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Scragmore
Scragmore 2012-1-27
评论： Manduna Watson 2014-6-30
Hi all.
I have two cell array's test1 240000x1 and test2 160000x1. Each cell of test1 contains a string, varying lengths 1-20 charicters. test2 is a list of unique entries from test1.
I wish to count the number of occurrences of each unique string in test2 in test1.
example strings in test1 & 2
test1 = {'ayooy'; 'ayta'; 'a'; 'aa'; 'aatl'; 'aatla'; ......};
test2 = {'a'; 'aa'; 'aaa'; 'aaaa'; 'aaaaa'; 'aaaac'; .......};
My code;
for ii = 1:length(test2)
b = ismember(test1,test2(ii,1));
test2{ii,2}(1,1) = sum(b);
end
Is there a way to speed this up or an alternative method that is faster. I know I am running a lookup that is 160k * 240k = 40,000 mill.
Thanks for you time
AD

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采纳的回答

Walter Roberson
Walter Roberson 2012-1-27
When you construct test2, use a different form of unique:
[test2, ua, ub] = unique(test1);
After that, the counts are:
test2counts = histc(ub, 1:length(test2));
  2 个评论
Scragmore
Scragmore 2012-1-28
Thanks for highlighting the additional output of unique and introducing me to new function histc. Worked a treat, supper fast compared to what I was originally doing.
Cheers,
AD
Manduna Watson
Manduna Watson 2014-6-30
Thank you, this really helped me to identify and count repeated characters in my data set

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