[R] Find each time a value changes

[Ben Tupper]

Hi,

On Feb 10, 2010, at 8:58 PM, Tim Clark wrote:

> Dear List,
>
> I am trying to find each time a value changes in a dataset.  The  
> numbers are variables for day vs. night values, so what I am really  
> getting is the daily sunrise and sunset.
>
> A simplified example is the following:
>
> x<-seq(1:100)
> y1<-rep(1,10)
> y2<-rep(2,10)
> y<-c(y1,y2,y1,y1,y1,y2,y1,y2,y1,y2)
> xy<-cbind(x,y)
>
>
> I would like to know each time the numbers change.
> Correct answer should be:
> x=1,11,21,51,61,71,81,91
>

I think this gets close...

which(diff(y) != 0)
[1] 10 20 50 60 70 80 90

You'll need to fiddle to get exactly what you want.

Cheers,
Ben



> I would appreciate any help or suggestions.  It seems like it should  
> be simple but I’m stuck!
>
> Thanks,
>
> Tim
>
>
> Tim Clark
> Department of Zoology
> University of Hawaii
>
>
>
>
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