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

Question

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

similarly for ther values of second column in matrix,,,,???please help

Answer 1

[r,~]=find(A==-1);
A=A(r,:)