Hi:
The head() function is helpful here:
(i) plyr::ddply()
library('plyr')
ddply(dat, .(id), function(d) head(d, 1))
id value
1 1 5
2 2 4
(ii) aggregate():
aggregate(value ~ id, data = dat, FUN = function(x) head(x, 1))
id value
1 1 5
2 2 4
The formula version of aggregate() requires R-2.11.0 +
Dennis
On Sun, Sep 25, 2011 at 1:22 PM, AC Del Re <de...@wisc.edu> wrote:
> Hi,
>
> I am trying to select the first row of a variable with data in long-format,
> e.g.,
>
> # sample data
> id <- c(1,1,1,2,2)
> value <- c(5,6,7,4,5)
> dat <- data.frame(id, value)
> dat
>
> How can I select/subset the first 'value' for each unique 'id'?
>
> Thanks,
>
> AC
>
> [[alternative HTML version deleted]]
>
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