addition loops in matlab

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ali hassan
ali hassan 2022-2-12
编辑： DGM 2022-2-12
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?
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ali hassan
ali hassan 2022-2-12
thanks a lot. i had the same in my mind. but i cant figure out for loop less answer.
Austin Decker
Austin Decker 2022-2-12
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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DGM
DGM 2022-2-12
编辑：DGM 2022-2-12
Ran in:
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
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ali hassan
ali hassan 2022-2-12
编辑：ali hassan 2022-2-12
thanks a lot @DGM. adding a bit twist here.
a = [1 nan 1 1 0 0 nan 1 1 nan 1];
suppose it contains nan as well. how can i do the same and ignore nan?
if i use movsum, nan will be removed but the entry will still be considered. how can i also make it to ignore nan entry as well?
DGM
DGM 2022-2-12
编辑：DGM 2022-2-12
Ran in:
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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