[R] help with rle function on paired data

[Peter Ehlers]

On 2012-06-08 14:33, Steve E. wrote:
> Dear R Community - I hope you might be able to provide some guidance
> regarding the use of the rle function. I have a set of time-series data
> where a measured value is recorded every 30 seconds after the start of an
> experiment. Many of the measured values repeat and I am interested only in
> the values when there is a change. If I turn the measured values into a
> vector, the rle function works perfectly for this but I need also the
> corresponding time of the value and I am not sure how to use rle on paired
> data. Below is a brief example to help explain the problem. I thank you in
> advance for any assistance you might be able to provide. Regards, Steve
>
> Original dataset:
>
> ElpsdTime, DataValue
> 0, 1
> 30, 1
> 60, 1
> 90, 2
> 120, 2
> 150, 3
> 180, 2
> 210, 3
> 240, 3
> .
> .
>
> Desired dataset:
>
> ElpTime	DataValue
> 0, 1
> 90, 2
> 150, 3
> 180, 2
> 210, 3
> .
> .

Let's call your dataframe 'dat'. Here's a pretty brute-force way:

   z <- rle(dat[, 2])
   zV <- z$values
   zL <- z$lengths
   idx <- c(0, head(cumsum(zL), -1)) + 1
   newdat <- data.frame(time = dat[idx, 1], value = zV)
   newdat

Peter Ehlers