[R] Speed Optimization: Faster Way of Accessing data.frame in a Loop?

[Prof Brian Ripley]

I don't see how this code can work at all. '[<-.data.frame' does not 
accept three arguments, e.g.

> women[1,2,3] <- 17
Error in `[<-.data.frame`(`*tmp*`, 1, 2, 3, value = 17) :
         unused argument(s) (3)

If df is in fact a three-dimensional array you can do

df[1:20, 1:30, 20] <- df[1:20, 1:30, 27] + df[1:20, 1:30, 30]

BTW, df is the pdf of the F distribution in R, so not a good choice for a 
variable name.


On Fri, 10 Nov 2006, Sven C. Koehler wrote:

> Hello,
>
> currently I am using code, which basically works like this:
>
> |
> | for (i in 1:20) {
> |   for (j in 1:30) {
> |     df[i, j, 20] <- df[i,j,27] + df[i,j,30]
> |   }
> | }
>
> df is:  `data.frame: 360 obs. of  30 variables'
>
> Do you have any ideas whether I could get this code any faster?
>
> Regards,
>
> Sven C. Koehler
>
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-- 
Brian D. Ripley,                  ripley at stats.ox.ac.uk
Professor of Applied Statistics,  http://www.stats.ox.ac.uk/~ripley/
University of Oxford,             Tel:  +44 1865 272861 (self)
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