While I agree with boftx that a real script would be more appropriate for something like this in a production setting, I appreciate that pushing one-liners to their limits can make for good learning exercises.

As for your splice based solution, I think that's actually pretty good. Here are two small suggestions to tweak it further:

  1. You can get rid of the  BEGIN { $"=":" }  by using  $_  instead of  "@F"  to refer to the original line.

  2. You can get rid of the separate  %line  hash by adding that information directly to  %h  whose contents would then look like: 
    (
  ZM => [ [20470, "20470:ZM:Samfya:Africa"],
          [20149, "20149:ZM:Sesheke:Africa"],
          [18638, "18638:ZM:Siavonga:Africa"] ],
  ZW => [ ... ],
  ...
)

    [download]

Here's the one-liner with those changes, in a "scriptified" representation (which I find easier to work with; it's trivial to convert it back to the one-liner format by removing the lines with comments after them):

use warnings;       # just for debugging
use strict;         # just for debugging
my (%h, $k, @F);    # just for debugging

while (<>) {        # -n
  chomp;            # -l
  $\ = "\n";        # -l
  @F = split(':');  # -F":" -a
  
  push @{$h{ $F[1] }}, [$F[0], $_];
}
for $k (sort keys %h) {
  print $_->[1] for splice [sort {$b->[0]<=>$a->[0]} @{$h{$k}}], 0, 4
}                   # -n

[download]

In reply to Re: Using map function to print few elements of list returned by sort function by smls
in thread Using map function to print few elements of list returned by sort function by jaypal

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