[R] Calculating First Occurance by a factor

[hadley wickham]

On Mon, Mar 30, 2009 at 2:58 PM, Mike Lawrence <Mike.Lawrence at dal.ca> wrote:
> I discovered Hadley Wickham's "plyr" package last week and have found
> it very useful in circumstances like this:
>
> library(plyr)
>
> firstfixtime = ddply(
>       .data = data
>       , .variables = c('Sub','Tr','IA')
>       , .fun <- function(df){
>               df$FixTime[which.min(df$FixInx)]
>       }
> )

Or to save a little typing:

ddply(data, .(Sub, Tr, IA), colwise(min, .(FixTime))

Hadley


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