sorting particular column of the matrix in stages and combining

Ex:pop= 1.023 4.016 3.012 9.012 1 20.012 5.092 3.412 6.801 0.234 1 02.013 3.001 8.903 7.091 5.001 1 12.012 0.001 2.364 5.023 3.333 1 06.001 0.111 5.905 0.221 4.012 2 41.670 2.345 6.980 4.992 6.001 2 06.123 6.020 4.019 7.012 1.034 2 13.000 8.010 3.012 6.321 2.234 2 14.333 sorting 1st(5th column) group i.e 6th column,sorting 2nd(5th column) group i.e 6th coulmn, finally combine. coding i have written A_11=0 for aa=1:8 if (pop(aa,5)==i)(i= 1,2,3,..) a11(aa,:)=pop(aa,:); end end pop1=sort(a11,'descend'); A_11=A_11+pop1(getting some error)

[rajesh kumar]

 i wanna sorting of 6th column 1 category in descending order,simillary
6th column of second category  and then combine.