@Kenn: Yeah I have a way of loosing concentration when fiddling around and
trying to get it work. Thanks for pointing out that I supplied a third
argument when I wanted an additional test in the second argument instead.
Also my selection choices indeed do not make any sense, no wonder your
"parser" flaked out.

@Jeff: Thanks for also pointing that out and for your tips on temporary
storage and clarification on aggregation. I will have a look into plyr.


Thank you both very much for your input.

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