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Speed up or alternative to 'For' loop

Mon, Jun 10, 2013 3:51 PM

Well, speaking of hasty...

This will also do it, provided that each tree's initial height is less
than the previous tree's final height. In principle, not a safe
assumption, but might be ok depending on where the data came from.

df$delta <- c(NA,diff(df$Height))
df$delta[df$delta < 0] <- NA

-Don

Don MacQueen

Lawrence Livermore National Laboratory
7000 East Ave., L-627
Livermore, CA 94550
925-423-1062





On 6/10/13 2:51 PM, "MacQueen, Don" <macqueen1 at llnl.gov> wrote:

>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
>
>
>-- 
>Don MacQueen
>
>Lawrence Livermore National Laboratory
>7000 East Ave., L-627
>Livermore, CA 94550
>925-423-1062
>
>
>
>
>
>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
>>option:
>>
>>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
>>https://stat.ethz.ch/mailman/listinfo/r-help
>>PLEASE do read the posting guide
>>http://www.R-project.org/posting-guide.html
>>and provide commented, minimal, self-contained, reproducible code.
>
>______________________________________________
>R-help at r-project.org mailing list
>https://stat.ethz.ch/mailman/listinfo/r-help
>PLEASE do read the posting guide
>http://www.R-project.org/posting-guide.html
>and provide commented, minimal, self-contained, reproducible code.

Thread (7 messages)

Trevor Walker Speed up or alternative to 'For' loop Jun 10 Rui Barradas Speed up or alternative to 'For' loop Jun 10 MacQueen, Don Speed up or alternative to 'For' loop Jun 10 David Winsemius Speed up or alternative to 'For' loop Jun 10 MacQueen, Don Speed up or alternative to 'For' loop Jun 10 MacQueen, Don Speed up or alternative to 'For' loop Jun 10 arun Speed up or alternative to 'For' loop Jun 10