Just for fun with Schwartzian transform and expensive sort!

  DB<109> $txt='id003;30;80;10'
 
  DB<110> local $.=0; @sort = sort {$a->[0] <=> $b->[0]} map { [$_ => 
+$.++] } split /;/, $txt 
 
  DB<111> print $sort[-1]->[1]
2
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Was to lazy to eliminate the id field first. :)