addition loops in matlab

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ali hassan
ali hassan on 12 Feb 2022
Edited: DGM on 12 Feb 2022
assume i have a vector array:
a=[1 1 1 0 0 1 1 1]
how can i put loop such that if sum of any three successive elements is equal to 3, it prints 'ali'.
can it be done without loops?
  3 Comments
Austin Decker
Austin Decker on 12 Feb 2022
Well, MATLAB is likely looping behind the scenes, but you could do this:
a = [1,1,1,0,0 1,1,1];
ind1 = 1:length(a) -2;
ind2 = ind1 + 2;
result = arrayfun(@(x,y) sum(a(x:y)),ind1,ind2);
qty = sum(result == 3);
disp(join(repmat("ali",qty,1),newline));

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Accepted Answer

DGM
DGM on 12 Feb 2022
Edited: DGM on 12 Feb 2022
This works easily enough. After R2016a, you can do the same with movsum().
a = [1 1 1 0 0 1 1 1];
if any(conv(a,[1 1 1],'valid')==3)
fprintf('ali\n')
end
ali
  4 Comments
DGM
DGM on 12 Feb 2022
Edited: DGM on 12 Feb 2022
To omit nans:
a = [2 nan 1 1 0 0 nan 1 1 nan 1];
% using movsum
s = movsum(a,3,'omitnan');
any(s(2:end-1)==3)
ans = logical
1
% using conv
a(isnan(a)) = 0;
s = conv(a,[1 1 1],'valid');
any(s==3)
ans = logical
1
If the value range of a never extends beyond [0 1], then you could also simply treat any propagated NaNs as 0. This is simply because it wouldn't be possible to have a sum equal to 3 if the window size were also 3 and any element were anything other than 1.
a = [1 nan 1 1 0 0 nan 1 1 nan 1];
s = conv(a,[1 1 1],'valid') % this will pass NaN
s = 1×9
NaN NaN 2 1 NaN NaN NaN NaN NaN
any(s==3) % NaNs aren't equal to 3
ans = logical
0

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