Here is one way:
> tmp1 <- data.frame(Species=c('setosa','virginica','versicolor'),
+ row=c(7,20,18) )
>
> tmp.iris <- iris
> tmp.iris$row <- ave(iris$Sepal.Length, iris$Species, FUN=seq_along)
>
> out.iris <- merge(tmp.iris, tmp1, by=c('Species','row'))
>
>
> out.iris
Species row Sepal.Length Sepal.Width Petal.Length Petal.Width
1 setosa 7 4.6 3.4 1.4 0.3
2 versicolor 18 5.8 2.7 4.1 1.0
3 virginica 20 6.0 2.2 5.0 1.5
>
Another way would be to use the split function on your big data set, then use
sapply to iterate over the list resulting and return just the rows from
failed.3 in each group. Need to think a bit more about how that would look.
You could also just loop through the rows of failed.3 and grab the
corresponding pieces in the full dataset.
There are probably a few other ways as well.
--
Gregory (Greg) L. Snow Ph.D.
Statistical Data Center
Intermountain Healthcare
greg.s...@imail.org
801.408.8111
> -----Original Message-----
> From: r-help-boun...@r-project.org [mailto:r-help-bounces@r-
> project.org] On Behalf Of Linh Tran
> Sent: Saturday, March 05, 2011 11:56 AM
> To: r-help@r-project.org
> Subject: [R] subsetting data by specified observation number
>
> Hi members,
>
> I'd like to thank you guys ahead of time for the help. I'm kind of
> stuck.
>
> I have a data frame with ID and position numbers:
> 1> head(failed.3)
> id position
> 1 10000997 2
> 4 1000RW_M 2
> 15 1006RW_G 2
> 24 1012RW_M 3
> 28 10160917 2
> 30 1016RW_M 13
>
> I'd like to use this to subset out a large dataset and keep only the
> observation number corresponding to the position number. So for
> example,
> ID 10000997 has 10 observations. I want to keep the 2nd one only.
>
>
> Thanks,
>
> -linh
>
> ______________________________________________
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