# How to extract the column first of matrix based on the values of the second column in the matrix??

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Mohammad Bhat on 15 Feb 2018
Edited: Birdman on 15 Feb 2018
Hi, I have a matrix (100 x2), I have to extract the sub-matrix on the basis of values in the second column e.g v =
31.1302569857687 -1
32.180318519244 -1
12.7872162725122 -1
13.2835575054275 -1
10.021621625266 -1
36.6009958880903 0
36.9774647589583 0
36.787129542817 0
38.7367125605671 0
40.100285535143 0
42.8454536678047 0
26.452464913501 0
19.5200640367802 0
19.245074694581 0
14.6551322068414 0
19.7294931511177 0
18.3170112190827 0
16.904818839609 0
16.1732155120743 0
13.5931195830832 0
11.4443392120297 0
15.1648574012419 0
19.0397715322427 0
22.1538461672009 0
21.4124473145878 0
27.5084150761181 0
32.1131265995698 0
36.8482414777151 0
41.5676905781401 0
46.4802420389567 0
51.5351617830002 0
51.4051835907625 0
52.6130487616903 0
45.4204018035948 1
58.9232797797271 1
55.494620460005 1
52.3197180802802 1
49.4474761742195 1
46.9334944362765 1
61.1522109166954 1
43.9118765256052 1
42.2508331278804 1
40.3429411421627 1
65.5795158567064 1
38.8385491490092 1
37.8963441508545 1
34.9973270407898 1
29.0715135484894 1
26.3543715538808 1
38.95578134244 1
23.0896708508372 1
22.7642900174813 1
35.1498634421245 1
31.3562258570766 1
24.5795219644321 1
24.7562699128928 1
21.6714766455819 1
21.45630210451 1
20.6129304078775 1
14.1022303200593 1
16.5497099672472 1
13.1488744765474 1
14.6932943889381 1
20.2729598233706 1
25.23 1
22.6374225564661 1
23.8778746960445 1
26.0356083086223 1
27.6852469737945 1
32.3693203512215 1
35.8534921590631 1
39.6632436898446 1
44.2794862210482 1
44.7746903953562 1
47.3547558329678 1
45.1999214601088 1
52.9772866424848 1
56.3786564224441 1
57.0621845007707 1
44.4008209383565 1
45.6003607441871 1
49.3203092042213 1
47.3169409408512 1
48.544751518573 1
53.2521633363378 1
56.5622922095631 1
59.3042401519487 1
51.4156872948325 1
66.4488743320758 2
62.2216433405612 2
58.6323536965727 2
51.0483388564212 2
47.0732716092689 2
11.0405117635008 2
13.4057040098609 2
12.9604359494579 2
18.4177333024452 2
23.171381055086 2
16.5587710896673 2
19.2045020763362 2
I have to extract the values or sub-matrix which are having specific values of second column e.g above I should get separate three sub matrices such as
31.1302569857687 -1
32.180318519244 -1
12.7872162725122 -1
13.2835575054275 -1
10.021621625266 -1

Birdman on 15 Feb 2018
[r,~]=find(A==-1);
A=A(r,:)
##### 2 CommentsShowHide 1 older comment
Birdman on 15 Feb 2018
Then you will change it to
[r,~]=find(A==0);
A=A(r,:)
or
[r,~]=find(A==1);
A=A(r,:)
and else. But if you want to automatically divide them according to the changes in second column, do this:
[~,idx,~]=unique(A(:,2));
idx=[idx.' size(A,1)];
for i=1:numel(idx)-1
B{i,1}=A(idx(i):idx(i+1)-1,:);
end
and you will store them in cell array since they have different dimensions.