classifying matrix value based on its element

All,

I have the following nx3 matrix. My question is how to classify these matrix based on the value in column 3, i.e. I want to group them based on the value that has similar values in column 3.

Please note that I may have hundreds of matrix similar to this one. I have produced the following code

    sig3 = data(:,3);
    sig3sort=zeros(length(sig3),1);
    for ii=2:length(sig3)
        if sig3(ii-1)==sig3(ii)
            sig3sort(ii) = nan;
        else
            sig3sort(ii) = sig3(ii);
        end
    end
    sig3sort = sig3sort(~isnan(sig3sort))

and wondering if someone can make it more elegant?

         201           5           5
         306          20           5
         301          40           5
         317          60           5
         320          80           5
         305         100           5
         231          10          10
         300          20          10
         328          40          10
         359          60          10
         353          80          10
         355         100          10
         430          20          20
         529          40          20
         551          60          20
         554          80          20
         560         100          20
         532         120          20
         575         140          20
         590         160          20
         601         180          20
         582         200          20
         605          40          40
         620          60          40
         700          80          40
         733         100          40
         720         120          40
         723         140          40
         731         160          40
         781         180          40
         755         200          40
         747          60          60
         811          80          60
         821         100          60
         835         120          60
         859         140          60
         860         160          60
         861         180          60
         861         180          60
         821         200          60
         889          80          80
         954         100          80
         962         120          80
         992         140          80
        1003         160          80
        1026         180          80
        1052         200          80
         998         220          80
        1005         240          80
         956         100         100
         975         120         100
        1012         140         100
        1067         160         100
        1089         180         100
        1155         200         100
        1106         220         100
        1098         312         100

Answer 1

[Aquatris]

Is this what you are trying to achieve;

    a = [201           5           5
         306          20           5
         301          40           5
         317          60           5
         320          80           5
         305         100           5
         231          10          10
         300          20          10
         328          40          10
         359          60          10
         353          80          10
         355         100          10
         430          20          20
         529          40          20
         551          60          20
         554          80          20
         560         100          20
         532         120          20
         575         140          20
         590         160          20
         601         180          20
         582         200          20
         605          40          40
         620          60          40
         700          80          40
         733         100          40
         720         120          40
         723         140          40
         731         160          40
         781         180          40
         755         200          40
         747          60          60
         811          80          60
         821         100          60
         835         120          60
         859         140          60
         860         160          60
         861         180          60
         861         180          60
         821         200          60
         889          80          80
         954         100          80
         962         120          80
         992         140          80
        1003         160          80
        1026         180          80
        1052         200          80
         998         220          80
        1005         240          80
         956         100         100
         975         120         100
        1012         140         100
        1067         160         100
        1089         180         100
        1155         200         100
        1106         220         100
        1098         312         100];

checks = unique(a(:,3));

for i = 1:length(checks)
  ind{i} = find(a(:,3) == checks(i));
end

group1 = a(ind{1},:);
group2 = a(ind{2},:);
...

[Aquatris]

This groups the rows that have the same value at the third column. Alternatively, you can put;

 group{i} = a(ind{i},:);

inside the for loop if you want to obtain the groups as a variable.

Answer 2

[Image Analyst]

Have you tried sortrows()?

sig3sorted = sortrows(data, 3);