[R] Aggregating a List
Peter Dalgaard BSA
p.dalgaard at biostat.ku.dk
Wed Nov 6 22:11:22 CET 2002
Paul Boutros <pcboutro at engmail.uwaterloo.ca> writes:
> Hi all,
>
> There must be a really obvious R solution to this, but I can't figure out
> how to aggregate a list. For instance, if I read.table the following from
> a file:
> Val1 Val2
> A 3 4
> A 5 6
> B 4 4
>
> I would like to take the mean (or median) across any/all rows of type "A"
> to end up with the structure:
>
> Val1 Val2
> A 4 5
> B 4 4
>
> in this case. How would I go about doign that w/o doing a loop or putting
> into a DB and using SQL to do this?
>
> Thanks for any suggestions, or pointers at appropriate functions I should
> be reading the documentation on.
aggregate()
E.g.,
> g <- read.table(stdin(),header=T)
0: gr Val1 Val2
1: A 3 4
2: A 5 6
3: B 4 4
4:
> g
gr Val1 Val2
1 A 3 4
2 A 5 6
3 B 4 4
> aggregate(g[-1],list(g$gr),mean)
Group.1 Val1 Val2
1 A 4 5
2 B 4 4
or for that matter: aggregate(g[-1],g[1],mean)
--
O__ ---- Peter Dalgaard Blegdamsvej 3
c/ /'_ --- Dept. of Biostatistics 2200 Cph. N
(*) \(*) -- University of Copenhagen Denmark Ph: (+45) 35327918
~~~~~~~~~~ - (p.dalgaard at biostat.ku.dk) FAX: (+45) 35327907
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