Thanks to Peter and Phil, this was indeed my idea. On Thu, Sep 25, 2008 at 2:26 PM, Peter Dalgaard <[EMAIL PROTECTED]> wrote: > 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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