The excellent formatting of the code doesn't make it easy to follow what's going on, but taking a wild guess, I would assume that timestamps are numeric, in which case you want to say sort {$a <=> $b} keys %timestamps

But that only begs the question, why don't you get Oracle to sort the data for you with an ORDER BY clause?

Something else to be said in passing: the normalisation of $date_value is better written as

  if ($data_name eq 'minutes') { $data_value = sprintf( '%9.2f', $data
+_value * 1440 ) };
  # or better yet
  $data_value = sprintf( '%9.2f', $data_value * 1440 ) if $data_name e
+q 'minutes';
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