Executing loop on certain numbers

Question

Raghavendra Reddy P 2015-5-11

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https://ww2.mathworks.cn/matlabcentral/answers/216138-executing-loop-on-certain-numbers

评论： Raghavendra Reddy P 2015-5-11

i have two vectors L=1:12; idx=[3 5 9]; I wanted to execute for loop for i=12:-1:1 now i want execute vector idx, starting from last elemet to first i.e 9,5,3 something like

    if i==9
        do stuff
    end
    if i==5
        do stuff 
    end
    .
    .
    if i==3
        do stuff
    end
end
i don't know how many elements in vector idx before hand.

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Answer 1

Stephen23 2015-5-11

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编辑：Stephen23 2015-5-11

在 MATLAB Online 中打开

You can execute over the vector backwards by using basic MATLAB indexing:

idx = [3,5,9];
for k = idx(end:-1:1)
    ... code here
end

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Stephen23 2015-5-11

编辑：Stephen23 2015-5-11

在 MATLAB Online 中打开

For a start you could use switch inside the loop:

for k = idx(end:-1:1)
    switch k
        case 9
            ... code
        case 5
            ... code
        case 3
            ... code
        otherwise
            error('This values is not known: %d',k)
    end
end

But, depending on what those calculations are, there might be much easier and faster ways of achieving this. If you tell us exactly what the do stuff operations actually are, then we might be able to tidy this up too. Can the the vector idx change, or is it always the same?

Raghavendra Reddy P 2015-5-11