[R] Find each time a value changes

[Tim Clark]

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 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