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

Asked by Giorgos Papakonstantinou on 21 Jun 2013

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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Giorgos Papakonstantinou

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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);

1 Comment

Giorgos Papakonstantinou on 21 Jun 2013

Thank you Andrei

Andrei Bobrov
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

Jan Simon on 22 Jun 2013

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.

Jan Simon
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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Image Analyst

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