$ echo '20470:ZM:Samfya:Africa
> 61739:ZW:Chinhoyi:Africa
> 20149:ZM:Sesheke:Africa
> 26459:ZW:Beitbridge:Africa
> 37423:ZW:Bindura:Africa
> 18638:ZM:Siavonga:Africa
> 699385:ZW:Bulawayo:Africa
> 47294:ZW:Chegutu:Africa
> 18860:ZW:Chipinge:Africa
> 28205:ZW:Chiredzi:Africa
> ' | perl  -F: -nale ' push @d, [@F];
>  END { print join "\n", map { join ":", @$_}
>  grep { $c = $$_[1] eq $prec? $c+1:1; $prec = $$_[1]; $c>4? 0: 1}
>  sort {$a->[1] cmp $b->[1] || $b->[0] <=> $a->[0]} @d;}'


20470:ZM:Samfya:Africa
20149:ZM:Sesheke:Africa
18638:ZM:Siavonga:Africa
699385:ZW:Bulawayo:Africa
61739:ZW:Chinhoyi:Africa
47294:ZW:Chegutu:Africa
37423:ZW:Bindura:Africa