[R] DROP OBSEVATION IN A GROUP

[Duncan Murdoch]

On 29/06/2011 4:29 PM, Peter Maclean wrote:
> People with more experience in R I need help on this.
> I would like to drop observation if they meet certain condition. In this example
> I would like to drop group 2 in "n" because the group in "Y" has more than 2
> zeroes.
> #Example
> n<- c(1, 1, 1, 1, 1, 1, 2, 2, 2, 2, 2, 2, 3, 3, 3, 3, 3,3)
> y<- c(2,3,2,3,4,5,6,1,0,0,0,6, 2, 1, 0, 0,9,3)
> z<- as.data.frame(cbind(n,y))
> colnames(z)<- c("n","y")

The general way to drop observations is to construct a logical vector to 
use as an index.  Entries which are FALSE are dropped.

Doing that based on your "more than 2 zeroes" rule looks a little 
tricky; I think you want to count zeros first (e.g. using by()), then 
construct the TRUE/FALSE vector based on that.

Duncan Murdoch

>
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