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How can I get a first value of each index from the other column?

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Jaehwi Bong
Jaehwi Bong am 24 Sep. 2019
Kommentiert: Rik am 24 Sep. 2019
I have this kind of data. First column and seconds column refer to an index and x value relatively.
data = [1 200; 1 201; 1 202; 1 201; 2 301; 2 313; 2 311; 3 401; 3 452; 3 433; 3 405; 4 504; 4 303; 4 604; 4 703; 5 600; 5 700; 5 606; 5 703; 5 905; 5 444;];
I want to have first value of 2nd colum of each index.
I'd like to have this kind of data that has half length (or tird whatever ratio) of index.
data = [1 200; 2 301;3 401;4 604;5 600;];
If anyone can help, it would be greatly appreciated.
Thank you!

Akzeptierte Antwort

Rik
Rik am 24 Sep. 2019
Use unique to get the list of first indices, the use either find or min in a loop.
  2 Kommentare
Jaehwi Bong
Jaehwi Bong am 24 Sep. 2019
Bearbeitet: Jaehwi Bong am 24 Sep. 2019
Thank you for your answer!
After I use the unique function, I'd like to get the corresponding values of second colum to the first value of first column. I don't want to use min.
for i = 1: max(col1)
col2(col1==i); %how can I get the 1st value of every iteration col2?
end
Could you give me advice again,please?
Rik
Rik am 24 Sep. 2019
This doesn't exactly match your output, but I suspect that could be a typo.
data = [1 200; 1 201; 1 202; 1 201; 2 301; 2 313; 2 311; 3 401; 3 452; 3 433; 3 405; 4 504; 4 303; 4 604; 4 703; 5 600; 5 700; 5 606; 5 703; 5 905; 5 444;];
col1=unique(data(:,1));
output=col1;
for n=1:numel(col1)
output(n,2)=data(find(data(:,1)==col1(n),1),2);
end
clc,disp(output)

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