[R] index and by groups statement

Robert Waters rwatersg at yahoo.com
Sun Aug 15 05:32:14 CEST 2004

Dear R-users

Im working with a dataset that contains information
for 8 groups of data and I need to select a sample of
certain size (100 cubic feet by group) from this
database for each of these 8 groups. To clarify, here
is the starting code Im working with:


However, I don't know how to specify in this code the
instruction: "by groups"

Does anyone have an idea how to do this?

Thanks in advance


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