use strict;

my @old = (237,153,258,231,154,159,141);
my %unique = map {$_ =>1} @old; #just in case the old rankins are not unique
my @ordered = sort keys %unique;
my %map = ();
for my $i (0..$#ordered){
	$map{$ordered[$i]} = $i+1;
}

foreach my $i (@old){
	print $i, "=>",$map{$i}/scalar(@ordered),"\n";
}
__END__
237=>0.857142857142857
153=>0.285714285714286
258=>1
231=>0.714285714285714
154=>0.428571428571429
159=>0.571428571428571
141=>0.142857142857143