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!

Answer 1

[Andrei Bobrov]

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);

[Giorgos Papakonstantinou]

Thank you Andrei

Answer 2

[Jan]

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)

[Giorgos Papakonstantinou]

Thank you Jan!

[Jan]

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 3

[Image Analyst]

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.