[R] Looking for a sort of tapply() to data frames

[January Weiner]

Hi,

I read about the by() function, but it does not seem to do the job I
need. Here is the problem:

Say - I have a data frame, with three columns.  The first one contains
strings that describe the data points, with repeats (for example, days
of a week).  The other two contain numbers. Something like that:

Day val1 val2
Tue 1    2
Tue 2    8
Tue 3    5
Wed 1    2
Wed 1    8
etc.

Now I would like to have a data frame with averages for each week:

Day val1 val2
Tue 2    5
Wed 1    5
etc.
I now I can do tapply(DF$val2, DF$days, mean) to get the means for
val2. But I would like to have a data frame as result (as in reality I
have many more columns).

Further question: where can I find a good, advanced introduction to R
data types? R's help() function just kills my brain, and the tutorials
are very limited.

My kind regards,

January Weiner

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------------ January Weiner 3  ---------------------+---------------
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