Compare two matrices of different dimensions

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Jonathan
Jonathan 2019-4-17
评论： Walter Roberson 2021-6-30
I have two matrices A=500000*4 and B=4300000*4.
Matrix A = id, plus 3 columns of NaN.
Matrix B = id, lat, lon, elev.
I would like to find the id values in A = B, and based on those same id values, fill matrix A with the missing lat,lon,elev.
The code I have is:
for i=1:length(A)
ind = B(:,1)==A(i,1);
A(i,2:4) = B(ind,2:4);
clear ind
end
This works but is extremely slow. How can I do this more efficiently?
Thanks
Jon

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采纳的回答

Jonathan
Jonathan 2019-4-17
I fiddled around with this further and addressed the loop, which was re-doing the "find" and settled on this...
C=A(:,1);
D=B(:,1);
idx=find(ismember(C,D));
A(:,2)=B(idx,2);
A(:,3)=B(idx,3);
A(:,4)=B(idx,4);
seems to work.
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Leonardo Monteiro de Carvalho
Leonardo Monteiro de Carvalho 2021-6-30
If I wanted to compare C and D to check, for example, if C is in between 2 values (in 2 different columns) of array D, how would I do that?
Walter Roberson
Walter Roberson 2021-6-30
Two fixed columns? Or any two columns? If it is any two columns, then is D guaranteed to be non-decreasing along the rows? What is the desired output?
And to confirm, C and D are 2D and C and D have the same number of rows but not necessarily the same number of columns?
Or is C a column vector with the same number of entries that D has rows and the task is to find out which column the value is in relative to the content of that row of D?
Is there some pattern to the way D is arranged?

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更多回答（1 个）

darova
darova 2019-4-17
ind = B(:,1)==A(i,1); % array of 5000000x1 logical
Try:
for i=1:length(A)
ind = find(B(:,1)==A(i,1),1,'first'); % one value
A(i,2:4) = B(ind,2:4);
% clear ind
end

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