[R] difference of two rows

[R Help]

You want to use tapply

?tapply

This is a simple example

dat = data.frame(a=sample(1:10,100,T),b=rnorm(100,0,1))
tapply(dat$b,dat$a,mean)

Hope that helps,
Sam

On Wed, Nov 25, 2009 at 11:55 AM, clion <birte_2 at hotmail.com> wrote:
>
> Dear R user,
> I'd like to calculate the difference of two rows, where "ID" is the same.
> eg.: I've got the following dataframe:
> ID YEAR
> 13 2007
> 15 2003
> 15 2006
> 15 2008
> 21 2006
> 21 2007
>
> and I'd like to get the difference, like this:
> ID YEAR     diff
> 13 2007      NA
> 15 2003       3
> 15 2006       2
> 15 2008      NA
> 21 2006       1
> 21 2007      NA
>
> that should be fairly easy...I hope
> Thanks for any helpful comments
> B.
>
>
>
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>
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