Vectorize a for loop

Question

Ramon Ticzon 2019-3-19

0
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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/450861-vectorize-a-for-loop

评论： Ramon Ticzon 2019-3-19

Hi. How can I speed up the process of my for loop code.

function [missingCase] = CaseChecking(bimage)
missingCase = '';
for img = 1:66
    mapList = xlsread('map.xlsx',img);
    counter=0;
    for i = 1:200
        if (~bimage(mapList(i,2),mapList(i,1)))
            counter=counter+1;
        end
    end
    if counter<50
        missingCase = img;
        break
    end
end

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Answer 1

Andrei Bobrov 2019-3-19

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https://ww2.mathworks.cn/matlabcentral/answers/450861-vectorize-a-for-loop#answer_366049

Please attach your data (bimage,map.xlsx - small example) as mat-file and xlsx-file.

ml = zeros(200,2,66);
for ii = 1:size(ml,3)
    ml(:,:,ii) = xlsread('map.xlsx',ii);
end
mlw = permute(ml(:,end:-1:1,:),[1,3,2]);
out = find(~bimage(sub2ind(size(bimage),mlw(:,:,1),mlw(:,:,2))) < 50,'first',1);

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Ramon Ticzon 2019-3-19

These are the sample files. Thank you

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Answer 2

Andrei Bobrov 2019-3-19

0
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/450861-vectorize-a-for-loop#answer_366070

Solution for attached data:

[~,sheets] = xlsfinfo('MapList.xlsx');
n = numel(sheets);
ml = cell(n,1);
for ii = 1:n
    ml{ii} = xlsread('MapList.xlsx',ii);
end
jj = repelem((1:n)',cellfun('size',ml,1));
A = cat(1,ml{:});
k = accumarray(jj,(1:size(A,1))',[],...
               @(x) sum(~bimage(sub2ind(size(bimage),A(x,2),A(x,1)))));
out = find(k < 50,'first',1);