Matthew Pettis wrote:
Hi,
I want to sort a data frame by multiple columns and then take the
first record in each unique level of the "by" group I used to sort the
data frame. Does someone have an example of how to do this?
Thanks,
Matt
Something like this
> aggregate(airquality,airquality["Month"],head,1)
Month Ozone Solar.R Wind Temp Month Day
1 5 41 190 7.4 67 5 1
2 6 NA 286 8.6 78 6 1
3 7 135 269 4.1 84 7 1
4 8 39 83 6.9 81 8 1
5 9 96 167 6.9 91 9 1
where you probably want to lose the first column.
or
> unsplit(lapply(split(aq,aq$Month), head,1),5:9)
Ozone Solar.R Wind Temp Month Day
1 41 190 7.4 67 5 1
32 NA 286 8.6 78 6 1
62 135 269 4.1 84 7 1
93 39 83 6.9 81 8 1
124 96 167 6.9 91 9 1
This also works, but the "tail" variant is harder:
> unsplit(lapply(split(aq,aq$Month), "[",1,),5:9)
--
O__ ---- Peter Dalgaard Øster Farimagsgade 5, Entr.B
c/ /'_ --- Dept. of Biostatistics PO Box 2099, 1014 Cph. K
(*) \(*) -- University of Copenhagen Denmark Ph: (+45) 35327918
~~~~~~~~~~ - ([EMAIL PROTECTED]) FAX: (+45) 35327907
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