Count instances of subarray inside array

For an array

A = [2,2,2,2];

I would like to count how many times [2,2] appears in A, using each value only in one possible pair.

For example,

numel(strfind(A,[2,2]))

returns 3.

But if each "2" is used only once, then we have only 2 instances, instead of 3.

A is not necessarily of all same elements or even-number size, it could be e.g. A = [1,2,3].

Is there a simple way to do that?

[KSSV]

Try reshape into n*2 array and use ismember with rows option.

[Mitsu]

I mean for this approach to work regardless of the size and elements, such as A = [1,2,3]. I edited the question to clarify.

Answer 1

[Turlough Hughes]

You could do the following:

b = A == 2; % binary indicating where A equal to 2
count = 0;
ii = 1;
while ii < numel(A)
    if b(ii+1) && b(ii)
        count = count + 1;
        ii = ii + 1;
    end
    ii = ii + 1;
end

When there is a match, the loop variable, ii, increments an extra time so that each "2" is only used once.

[Turlough Hughes]

This assumes that A is a row as presented in the question. If A is a matrix though you can transpose it beforehand. e.g.

b = A.' == 2;

[Mitsu]

Thank you. There might be no other way around but to do it following the logic in your answer. For now I will wait to see if there are other answers with simpler, maybe one-line, approach.

[Turlough Hughes]

Another way would be to get the length of each group of twos (based on this answer by @Image Analyst) and then round down each group's length to the nearest whole number divisible by two:

measurements = regionprops(A == 2, 'Area');
allLengths = [measurements.Area];
count = sum(floor(allLengths/2))

(if you have the image processing toolbox)