Something like this (not tested)? df$diffP <- c(NA, NA, diff(df$P,2))
-Don -- Don MacQueen Lawrence Livermore National Laboratory 7000 East Ave., L-627 Livermore, CA 94550 925-423-1062 On 1/6/12 6:39 AM, "ikuzar" <raz...@hotmail.fr> wrote: >Hello, > >I created a data.frame which contains two columns: df$P (Power) et >df$DateTime (time). I'd like to add a new column df$diffP (difference of >Power between T and T-2). > >I made a loop : > >for (i in 3:length(df$DateTime)){ > df$diffP[i] = df$P[i] - df$P[i-2] >} >execution time result is unaceptable: 24s !! > >Is there any way to reduce complexity about O(n) ? for example 2 or 3s >(10s >maxi) > >Does anybody find better than ~24s ? > >thanks for your help > >-- >View this message in context: >http://r.789695.n4.nabble.com/data-frame-temporal-complexity-tp4269585p426 >9585.html >Sent from the R help mailing list archive at Nabble.com. > >______________________________________________ >R-help@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@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.