[R] data.frame: temporal complexity

[MacQueen, Don]

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" <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:
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>9585.html
>Sent from the R help mailing list archive at Nabble.com.
>
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