counting strings in cell array, is there a faster solution

Question

Scragmore 2012-1-27

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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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Answer 1

Walter Roberson 2012-1-27

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在 MATLAB Online 中打开

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));

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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 2014-6-30