use strict;
use warnings;

my %data;
{
   my $chrom;
   while (<DATA>) {
      chomp;
      if (/^variableStep chrom=(\S+)/) {
         $chrom = $1;
      } else {
         my ($tag, $value) = split;
         push @{ $data{$chrom} }, [ $tag, $value ];
      }
   }
}

for (
   [qw( chr1  9837  9840 )],
   [qw( chr1 99998 99999 )],
   [qw( chr2  9838  9840 )],
) {
   my ($chrom, $start, $stop) = @$_;

   my $chrom_d = $data{$chrom};

   my $count;
   my $sum;
   for (@$chrom_d) {
      my ($tag, $value) = @$_;
      next if $tag < $start || $tag > $stop;
      ++$count;
      $sum += $value;
   }

   if ($count) {
      my $avg = $sum/$count;
      print("$chrom $start..$stop average: $avg\n");
   } else {
      print("$chrom $start..$stop average: NA\n");
   }
}

__DATA__
variableStep chrom=chr1
9837    0.010
9838    0.008
9839    0.007
9840    0.004
9841    0.002
9842    0.001
variableStep chrom=chr2
9837    0.090
9838    0.038
9839    0.017
9840    0.044
9841    0.052
9842    0.091

##</code><code>##

chr1 9837..9840 average: 0.00725
chr1 99998..99999 average: NA
chr2 9838..9840 average: 0.033