push @{ $hash{ $header[$_] } }, $columns[$_] for 1 .. $#columns;
      ^            ^                 ^            ^    ^
      |            |                 |            |    |
      |            |                 |            |    + - To the last index
      |            |                 |            + - Starting at the next index after the index for ID
      |            |                 + - Column value
      |            + - Column heading
      + - Generate a HoA, where: keys are column names; values are references to lists of column entries