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Count the "areas" of zeros and the "areas" of ones in a vector?

I have a vector:

a=[0 1 1 1 1 1 1 0 0 1 1 1 1 1 0 0 1 1 1 0 1 ];

in which I would like to count the "areas" of zeros and the "areas" of ones. In the example above I have

4 areas of zeros and 4 areas of ones. Thank you!

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3 Answers

Answer by Andrei Bobrov
on 21 Jun 2013
 Accepted answer

a=[0 1 1 1 1 1 1 0 0 1 1 1 1 1 0 0 1 1 1 0 1 ];
lc = [true;diff(a(:))~=0];
x = a(lc);
zerosareas = sum(~x);
onesareas = sum(x);

Answer by Jan Simon
on 21 Jun 2013

Another approach which might be faster for large data sets: FEX: RunLength:

a = [0 1 1 1 1 1 1 0 0 1 1 1 1 1 0 0 1 1 1 0 1 ];
b = RunLength(a);
nZero = sum(b == 0);
nOne  = length(b) - nZero;  % Or: sum(b == 1)

  2 Comments

For 100'000 elements, the RunLength approach is twice as fast as the DIFF method. But as long as both methods need only some milliseconds, this might not really matter.


Answer by Image Analyst
on 23 Jun 2013

I know you already accepted an answer, but if you have the Image Processing Toolbox there is a straightforward one-liner solution to get either of those numbers:

a=[0 1 1 1 1 1 1 0 0 1 1 1 1 1 0 0 1 1 1 0 1];
[~, numberOf1Regions] = bwlabel(a)      % Get # of "1" regions.
[~, numberOf0Regions] = bwlabel(~a)     % Get # of "0" regions.

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