[R] Speed up or alternative to 'For' loop

MacQueen, Don macqueen1 at llnl.gov
Mon Jun 10 23:51:04 CEST 2013

How about

for (ir in unique(df$TreeID)) {
  in.ir <- df$TreeID == ir
  df$HeightGrowth[in.ir] <- cumsum(df$Height[in.ir])

Seemed fast enough to me.

In R, it is generally good to look for ways to operate on entire vectors
or arrays, rather than element by element within them. The cumsum()
function does that in this example.


Don MacQueen

Lawrence Livermore National Laboratory
7000 East Ave., L-627
Livermore, CA 94550

On 6/10/13 10:28 AM, "Trevor Walker" <trevordaviswalker at gmail.com> wrote:

>I have a For loop that is quite slow and am wondering if there is a faster
>df <- data.frame(TreeID=rep(1:500,each=20), Age=rep(seq(1,20,1),500))
>df$Height <- exp(-0.1 + 0.2*df$Age)
>df$HeightGrowth <- NA   #intialize with NA
>for (i in 2:nrow(df))
> {if(df$TreeID[i]==df$TreeID[i-1])
>  {df$HeightGrowth[i] <- df$Height[i]-df$Height[i-1]
>  }
> }
>Trevor Walker
>Email: trevordaviswalker at gmail.com
>	[[alternative HTML version deleted]]
>R-help at r-project.org mailing list
>PLEASE do read the posting guide
>and provide commented, minimal, self-contained, reproducible code.

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