Count the sequence of same values in an array until an new value comes up

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J.P. 2016-12-17

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评论： Image Analyst 2022-12-1

Hello everybody!

I need to count every sequence of same values, until a new, different sequence of a value comes up. Then, I need to count the new sequence.

As example: My row is 00000001111-1-1-1-1-1000111

I want to get a table saying:

Element: 0 1 -1 Count: 2 2 1

This means that I have 2 sequences of zeros, two sequences of ones and one sequence of minus ones.

I don't need to count each value, just the sequence until the next sequnece of values!

Thank you.

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dpb 2016-12-17

Bruno Luong has a runs-counting submittal at FileExchange that'll probably be just the ticket...

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Answer 1

the cyclist 2016-12-17

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编辑：the cyclist 2016-12-17

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Get RunLength from the File Exchange.

Then,

x = RunLength([0 0 0 1 1 -1 -1 0 0 1 1 ]);
u = unique(x); % The unique values
c = histcounts(x,[u Inf]); The number of sequences of those unique values

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Answer 2

Jan 2016-12-18

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编辑：Jan 2016-12-18

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Simpler than RunLength, because the sequence length does not matter:

x = [0 0 0 1 1 -1 -1 0 0 1 1 ];
B = x([diff(x)~=0, true]);
u = unique(B); % The unique values
c = histcounts(x, [u, Inf]);

The calculation of B is slower then with RunLength.mex, but if runtime is not the problem in your case, you can save the time and effort for compiling.

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Reji G 2022-12-1

How to count number of zeros(or any other particular number) alone?

Image Analyst 2022-12-1

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@Reji G here are some ways

x = [0 0 0 1 1 -1 -1 0 0 1 1 ];
numZeros = nnz(x == 0)
numZeros = 5
numZeros = numel(x) - nnz(x)
numZeros = 5
numZeros = sum(x == 0, 'all')
numZeros = 5

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Answer 3

Image Analyst 2016-12-18

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This is trivial (4 lines of code) with bwlabel of the Image Processing Toolbox which counts regions:

   m = [0 0 0 0 0 0 0 1 1 1 1 -1 -1 -1 -1 -1 0 0 0 1 1 1] % Instantiate sample data.
   uniquem = unique(m)
   for k = 1 : length(uniquem)
     [labeledData, counts(k)] = bwlabel(m == uniquem(k));
   end
   % Done!  Now show to command window so we can see the results.
   counts % Shows 1,2,2 for number of regions for -1, 0, 1