Using find to compare matrices

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MiauMiau 2012-12-12

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Hi

I have a matrix where the first column contains id's and the second some sort of information about thes id's, as an example such as below. What I want to do now, is to be able to say which information belongs to which id, for instance, for the example below, the id 1 has the "values" 5 and 9. So I would like to write code such that I could return for each id it's values. Now I have written that:

Y = [1,2,3,3,1; 5,6,7,8,9]'
 U = unique(Y(:,1)) 
for i= 1:length(U) 
  [A B] =  find(U(i)==Y(:,1)) 
end

Where the column with the 1,2,3,3,1 is storing these id's. Does that make any sense? What do I actually get returned in the [A B]?

Thanks a lot

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Answer 1

Thomas 2012-12-12

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编辑：Thomas 2012-12-12

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You do not need find

Y = [1,2,3,3,1; 5,6,7,8,9]'
Y((Y(:,1)==1),2)   % id =1
Y((Y(:,1)==2),2)   % id=2
Y((Y(:,1)==3),2)   % id=3

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MiauMiau 2012-12-12

Is that not almost the same thing, as I did in the very beginning if I may ask? What is returned to [A B] in my case?

Thomas 2012-12-12

编辑：Thomas 2012-12-12

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In your case it give the row and column number as answers to the find

eg for id=1

you get

i.e. 1 is present in y in row 1 column 1 and row 5 column 1

the generic form of find is

[row,col] = find(X, ...)

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Answer 2

MiauMiau 2012-12-12

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Thanks very much!

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Answer 3

MiauMiau 2012-12-12

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hi I have realized it still does not do what I wanted. Here I just get "7 8" as outputs. But I want to be able to get the values of each id. This means:

1001 -> 5 1010 -> 6

etc. etc.