Finding couple of values in other vector of values

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Ouatehaouks
Ouatehaouks 2021-12-21
评论： Ouatehaouks 2021-12-23
Say I have a list of couple of values and another list of couple of values which belong to Xd,Yd but that I don't know. How do I efficiently get the list of index locating xv,yv in Xd,Yd ?
All I could find so far is using a loop which is very slow...
[Xd,Yd] = meshgrid(linspace(0,100,101),linspace(0,100,101));
Xd=Xd(:);
Yd=Yd(:);
xv = randi(101,[20,1]);
yv = randi(101,[20,1]);
for i=1:length(xv)
Iv(i) = find(ismember(Xd,xv(i)) & ismember(Yd,yv(i))==1);
end
EDIT : this is a dummy exemple. I need to do that with a very long vectors of values.

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采纳的回答

Ouatehaouks
Ouatehaouks 2021-12-23
% I have three vectors of values vi on different zones (xi,yi) with overlapping areas i.e. they share some
% exact positions
% I build the global domain
Xd = [x1 x2 x3];
Yd = [y1 y2 y3];
% I remove the duplicates
[~,inds,~] = unique([Xd,Yd],'rows','stable');
Xd = Xd(inds);
Yd = Yd(inds);
% I put each zone on the global domain
% this means that I need to find where (xi,yi) are locatedd in (Xd,Yd)
% hence the ismember over all couples
v1g = nan(size(Xd));
Iin = ismember([Xd,Yd],[x1,y1],'rows')
v1g(Iin) = v1;
v2g = nan(size(Xd));
Iin = ismember([Xd,Yd],[x2,y2],'rows')
v2g(Iin) = v2;
v3g = nan(size(Xd));
Iin = ismember([Xd,Yd],[x3,y3],'rows')
v3g(Iin) = v3;
% I get the mean
meand = mean([v1g v2g v3g],2,'omitnan');

更多回答（1 个）

Image Analyst
Image Analyst 2021-12-21
Ran in:
Takes 1 millisecond (0.000897 seconds) on my computer. Why is that not fast enough for you?
There is a problem with the code in that sometimes it finds no match. What do you want to do in that situation? Here is a suggestion:
[Xd,Yd] = meshgrid(linspace(0,100,101),linspace(0,100,101));
Xd=Xd(:);
Yd=Yd(:);
xv = randi(101,[20,1]);
yv = randi(101,[20,1]);
tic
Iv = nan(length(xv), 1);
for k = 1 : length(xv)
locations = find(ismember(Xd,xv(k)) & ismember(Yd,yv(k))==1);
if ~isempty(locations)
Iv(k) = locations;
end
end
toc
Elapsed time is 0.013204 seconds.
  6 个评论
显示 4更早的评论
Image Analyst
Image Analyst 2021-12-21
I'm not sure I'm visualizing this correctly. Do you have a diagram?
Maybe unique([x,y,z], 'rows') could help you identify duplicates and unique rows.
Ouatehaouks
Ouatehaouks 2021-12-23
This is indeed what I do to remove the duplicate and I realized I actually can do the same with ismember....so thank you, the results are now given almost instantaneously ! I added the complete answer below.

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