how to extract another matrix out of a big matrix

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farfar
farfar 2017-9-11
评论： farfar 2017-9-11
Hello I have a big matrix including many rows and 2 columns. first column is the wavelengths. I need to extract another matrix out of it based on some specific wavelength value and I dont need the rest of data. for example this is my main matrix:
A=[420 0.23;421 0.26;422 0.25;423 0.24;424 0.28;425 0.27]
but I know that I just need values corresponding to (420 422 425) in the first column , so what i need is:
B=[420 0.23;422 0.25;425 0.27]
how can I ask to extract data for these three specific values in the first column? I cant refer to them by their position in matrix since it is not fix. thanks !

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采纳的回答

James Tursa
James Tursa 2017-9-11
v = [420,422,425];
B = A(ismember(A(:,1),v),:);

更多回答（1 个）

Stephen23
Stephen23 2017-9-11
>> A=[420 0.23;421 0.26;422 0.25;423 0.24;424 0.28;425 0.27]
A =
420 0.23
421 0.26
422 0.25
423 0.24
424 0.28
425 0.27
>> idx = ismember(A(:,1),[420,422,425]);
>> A(idx,:)
ans =
420 0.23
422 0.25
425 0.27

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