Simplifying for-find loop functions to speed up processing

Question

Cameron 2024-1-26

0
链接

此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/2074761-simplifying-for-find-loop-functions-to-speed-up-processing

编辑： Cameron 2024-1-26

Hi all,

A pretty basic question, but I'm trying to find a more elegant solution to search through a 750,000x5 list to remove entries from a corresponding list when more than three value in any respective row are above a threshold of 10. The long way of doing so that I have is

    % mD is a 750000 x 5 matrix containing distances to the nearest 5
    % neighbors of the r,c,v point (from knnsearch) in each row
    
    for i = size(r,1):-1:1
        if size(find(mD(i,:)>10),2) > 3
            r(i) = [];
            c(i) = [];
            v(i) = [];
        end
    end

4 个评论
显示 2更早的评论隐藏 2更早的评论

Torsten 2024-1-26

Are there more than 3 values in mD row (i) above 10?

But you don't refer to row i of mD in your loop - you refer to the complete matrix mD with your find-command.

Cameron 2024-1-26

Oops, good catch, that's my mistake, that should be mD(i,:)

请先登录，再进行评论。

请先登录，再回答此问题。

Answer 1

Dyuman Joshi 2024-1-26

1
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/2074761-simplifying-for-find-loop-functions-to-speed-up-processing#answer_1397936

编辑：Dyuman Joshi 2024-1-26

在 MATLAB Online 中打开

I assume r, c and v have the same number of rows -

%Check which rows from the given range in mD have more than 3 values greater than 10
idx = sum(mD(1:size(r,1),:)>10, 2)>3
%perform deletion
r(idx) = [];
c(idx) = [];
v(idx) = [];

If all the variables have the same number or rows then you can remove the indices used and just use mD.

0 个评论
显示 -2更早的评论隐藏 -2更早的评论

请先登录，再进行评论。

Answer 2

Cameron 2024-1-26

0
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/2074761-simplifying-for-find-loop-functions-to-speed-up-processing#answer_1397931

编辑：Cameron 2024-1-26

在 MATLAB Online 中打开

I've developed a better solution to the above, which is

    [~,mD] = knnsearch(rcv,rcv,'K',5);
    mD_thresh = find(mD>10);
    [row,~] = ind2sub(size(mD),mD_thresh);
    for i = 1:size(row,1)
        rcv(i,:) = [];
    end

This only takes a few seconds to run, but it sacrifices testing whether more than 3 values in the row are over the 10 threshold, and just deletes any row with a single value over the limit (preferable to a 200 hour run though). I also still feel there's a way to eliminate that for loop.