[R] data.frame: temporal complexity

[Bert Gunter]

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 <razuki at 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 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.



-- 

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