Hello Perl Monks, I have a following data set where I would like to print top 4 populated cities for each country. The data is not sorted so I'll have to sort the data first and then grab the top 4 populated cities for each country. The first column is population, second column is country, third column is city and forth being the continent. 

20470:ZM:Samfya:Africa
20149:ZM:Sesheke:Africa
18638:ZM:Siavonga:Africa
26459:ZW:Beitbridge:Africa
37423:ZW:Bindura:Africa
699385:ZW:Bulawayo:Africa
47294:ZW:Chegutu:Africa
61739:ZW:Chinhoyi:Africa
18860:ZW:Chipinge:Africa
28205:ZW:Chiredzi:Africa

[download]

So my output from the above data set would be: 

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

[download]

I was able to write a perl script to get me my desired output. Here is my attempt at the perl script. 

#!/usr/local/bin/perl

use strict;
use warnings;
use Data::Dumper;

my (%HoA, %lines);

while (my $line = <DATA>) {
    my ($value, $key) = split /:/, $line, 3;
    push @{$HoA{$key}}, $value;
    $lines{"$key $value"} = $line          # This could be done better
}

for my $country (keys %HoA) {
    my @list = sort { $b <=> $a } @{$HoA{$country}};  # This could be 
+done better
    for my $ind (0 .. 3) {    # This could be done better
        my $popu = $list[$ind] or next;
        print $lines{"$country $popu"};
    }
}

__DATA__
20470:ZM:Samfya:Africa
20149:ZM:Sesheke:Africa
18638:ZM:Siavonga:Africa
26459:ZW:Beitbridge:Africa
37423:ZW:Bindura:Africa
699385:ZW:Bulawayo:Africa
47294:ZW:Chegutu:Africa
61739:ZW:Chinhoyi:Africa
18860:ZW:Chipinge:Africa
28205:ZW:Chiredzi:Africa

[download]

My question is based on my attempt to try an write a one-liner equivalent of the above script. 

perl -F":" -lane '
BEGIN { $"=":" }
push @{$h{$F[1]}}, $F[0];
$line{$F[1],$F[0]} = "@F"; }{
for $k (keys %h) { print @$_ for map [ $line{$k,$_} ], sort { $b <=> $
+a } @{$h{$k}} }' file
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
28205:ZW:Chiredzi:Africa
26459:ZW:Beitbridge:Africa
18860:ZW:Chipinge:Africa

[download]

I am stuck at being able to print the just the top 4 entries using map function. The above just prints out entire file in sorted format.

I was hoping to get some advice from the monks here on both my perl script (for anything I could have done better) as well as solving the question on my one-liner attempt. I have added comments where I felt, I could have written it more idiomatically.

The above data was taken from a question posted on StackOverflow. I know one-liner are not the best way to approach problem but I am still learning perl and feel that writing one liners can help me clear concepts of perl functions. Also probably as I have written a lot of awk one-liners, I feel perl can do this as well.

Looking forward to your comments and suggestions.

Regards
Jaypal

Update: I was able to get the desired output using a splice. 


perl -F":" -lane '
BEGIN { $"=":" }
push @{$h{$F[1]}}, $F[0];
$line{$F[1],$F[0]} = "@F"; }{
for $k (keys %h) { print $line{$k,$_} for splice [sort { $b <=> $a } @
+{$h{$k}}] , 0, 4 }' file
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

[download]

However would appreciate if anyone can suggest a better approach.

In reply to Using map function to print few elements of list returned by sort function by jaypal

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