Remove rows in matrix A if not member of matrix B

Question

Lulu Dulac 2017-6-30

评论： Lulu Dulac 2017-6-30

Hi all,

I have two matrices, and I am trying to remove rows in one for numbers which are not part of the other. Below is my attempt:

trials;
for x = 1:256
    if ~ismember(trials,x);
       rows2remove=[x];
       imagesAll(rows2remove,:)=[];
    end 
%     imagesCut = 
end

But it is not working and I get the following error message (I guess because it keeps deleting rows?):

Matrix index is out of range for deletion.
Error in samplecode (line 21)
       imagesAll(rows2remove,:)=[];

Please could anyone help me with my code? Many thanks

Answer 1

Stephen23 2017-6-30

编辑：Stephen23 2017-6-30

MATLAB works best when working on entire arrays at once, whereas using a loop and removing rows like that is inefficient and not recommended.

>> tryIdx = [2,5,7,8];
>> allIdx = 1:size(imagesAll,1);

Method one: setdiff:

>> idx = setdiff(allIdx,tryIdx)
idx =
   1   3   4   6   9

Method two: ismember:

>> idx = ~ismember(allIdx,tryIdx)
idx =
1  0  1  1  0  1  0  0  1

And then simply:

imagesAll(idx,:)

Stephen23 2017-6-30

编辑：Stephen23 2017-6-30

@Lulu Duvec: given your new description, it seems that simple indexing will do what you want:

imagesAll(trials,:)

Lulu Dulac 2017-6-30

Thank you a lot!