Creating an efficient for loop

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Cary 2015-8-17

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/234085-creating-an-efficient-for-loop

评论： Star Strider 2015-8-17

for i = 1:length(startIdx)
    for j = 1:length(date(startIdx(i):cutoffIdx(i)))
        k = date(startIdx(i):cutoffIdx(i));
        try
            shortIdx(j)=find(and(and(and(and(and(jam>=1.2,jam<=2.3),expiration==xDates(i)),option_type=='c'),jamSym==1),quote_date==k(j)),1);
        catch
            warning('Not present')
            shortIdx(j)=0;
        end
    end
end

Let's say i = 1:4. On the first pass through i, everything is fine. But when i = 2, I am overwriting the stored shortIdx data I created when i was 1. j is the length of each i, and k is the dates for each i. Where I get tripped up is the last part of the try statement

quote_date==k(j)

because when i turns to 2, j is reset to 1. So even though k is the correct set of dates for i, I am simply overwriting the shortIdx variable, instead of appending to it. Is there a way for me to solve this efficiently? Or do I need to create an independent for loop for each i? Thank you.

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Answer 1

Star Strider 2015-8-17

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I can’t run your code, but if ‘shortIdx’ is a single value (likely an index, considering the find call), one (probably the easiest) solution is to create a matrix out of ‘shortIdx’ so it increments with both ‘i’ and ‘j’:

shortIdx(i,j) = ...;

and then refer to it by both indices in your catch block.