Chimpmunk's answer does work since a string in perl that begins with a number will act like a number in numeric situations. 
$str = "0.56HI There!";
$str += 10;
# $str now is "10.56"

[download]
That will set off warnings though. (as well it should)
If you don't want to do a split, you can do this ugly piece of code. 
sub bypre {
  substr($b,0,index($b,"+")) <=> substr($a,0,index($a,"+"));
}

[download]
Update: Read Fastolfe's note and other people's suggestion of cmp

In reply to Re: Numerically sorting array items containing delimited strings by lemming
in thread Numerically sorting array items containing delimited strings by ti-source

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