Why linear search? hehehe, snicker :)

#!/usr/bin/perl

# http://perlmonks.org/?node_id=1127420

use Search::Dict;
use warnings;
use strict;

my $max = 0;
my $file = join '', map s/(\S*)$/ $max += $1 /er, <DATA>;

open my $fh, '<', \$file or die "open failure $!";
my $picker = sub
  {
  look $fh, rand $max, {comp => sub {shift =~ s/.* //r <=> shift}};
  (split ' ', <$fh>)[0];
  };

my %tally;                               # now test it
$tally{$picker->()}++ for 1 .. 1e4;
use YAML; print Dump \%tally;

__DATA__
A 1e-7
B 20e-7
C 10e-5
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