moritz's approach is the same I had in mind, but there's something else that you should care about: if the dataset contains dates for different months and years, you could run out of resources quite easily (i.e. too many open files).

In these cases, FileCache is your friend ;-)

In reply to Re^3: How can you check to see if a file handle is already open? by alexm
in thread How can you check to see if a file handle is already open? by agent_smith

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