Can this data be made available via a database (mySql or SQLite?) instead? The tasks you request are really very easy in SQL.

You could take the tab-delimited file and convert to a CSV file and then use DBI and DBD::CSV (also see the Tutorials) ...
(Update: DBD::AnyData can be used to read your tab-delimited data as-is ; You can even construct in-memory tables from a string!)

Example SQL statements: 
  SELECT ... FROM your_table ORDER BY in, out;
  SELECT day, SUM(in + out) FROM your_table GROUP BY day;

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In reply to Re: Tabular Data, Group By Functions by davidrw
in thread Tabular Data, Group By Functions by Anonymous Monk

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