1. You are doing exactly what one is recommended to avoid in R. Have you read an Introduction to R? -- especially about "vectorization"?
2. To answer your question: ?diff It will probably be an order or 2 of magnitude faster. -- Bert On Fri, Jan 6, 2012 at 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-tp4269585p4269585.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. -- Bert Gunter Genentech Nonclinical Biostatistics Internal Contact Info: Phone: 467-7374 Website: http://pharmadevelopment.roche.com/index/pdb/pdb-functional-groups/pdb-biostatistics/pdb-ncb-home.htm ______________________________________________ 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.