addition loops in matlab

Question

ali hassan 2022-2-12

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1648220-addition-loops-in-matlab

编辑： DGM 2022-2-12

采纳的回答： DGM

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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 2022-2-12

thanks a lot. i had the same in my mind. but i cant figure out for loop less answer.

Austin Decker 2022-2-12

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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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Answer 1

DGM 2022-2-12

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https://ww2.mathworks.cn/matlabcentral/answers/1648220-addition-loops-in-matlab#answer_894445

编辑：DGM 2022-2-12

在 MATLAB Online 中打开

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 2022-2-12

编辑：ali hassan 2022-2-12

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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 2022-2-12

编辑：DGM 2022-2-12

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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