One thing you might consider when working with large dataframes is that
instead of partitioning the dataframe into smaller ones, create a list of
indices and use that to access the subset. Works especially well when using
'lapply' to cromp through many segments of a data frame:
> y
suid month esr
1 1074034 12 6
2 1074034 1 2
3 1074034 2 2
4 1074034 3 2
5 1074034 12 1
6 1074034 1 1
7 1074034 2 1
8 1074034 3 1
9 1074034 12 2
10 1074034 1 2
11 1074034 2 2
12 1074034 3 2
13 1074034 12 9
14 1074034 1 9
15 1074034 2 9
16 1074034 3 9
17 1123003 12 2
18 1123003 1 2
19 1123003 2 2
20 1123003 3 2
> y.ind <- split(seq(nrow(y)), y$month)
> y.ind
$`1`
[1] 2 6 10 14 18
$`2`
[1] 3 7 11 15 19
$`3`
[1] 4 8 12 16 20
$`12`
[1] 1 5 9 13 17
> # a subset
> y[y.ind[['12']],]
suid month esr
1 1074034 12 6
5 1074034 12 1
9 1074034 12 2
13 1074034 12 9
17 1123003 12 2
>
On Wed, Jun 24, 2009 at 11:34 PM, Stephan Lindner <lindn...@umich.edu>wrote:
> Dear all,
>
>
> I have a code where I subset a data frame to match entries within
> levels of an factor (actually, the full script uses three difference
> factors do do that). I'm very happy with the precision with which I can
> work with R, but since I loop over factor levels, and the data frame is
> big, the process is slow. So I've been trying to speed up the process
> using by(), but I got stuck at the point where I want to stack back
> the sub- data frames, and I was wondering whether someone could help me
> out.
>
> Here is an example:
>
> <--
>
> > y <- data.frame(suid = c(rep(1074034,16),rep(1123003,4)),
> month = rep(c(12,1,2,3),5),
> esr = c(6,2,2,2,1,1,1,1,2,2,2,2,9,9,9,9,2,2,2,2))
>
>
> > by(y,y$month,function(x)return(x))
>
> y$month: 1
> suid month esr
> 2 1074034 1 2
> 6 1074034 1 1
> 10 1074034 1 2
> 14 1074034 1 9
> 18 1123003 1 2
> ------------------------------------------------------------
> y$month: 2
> suid month esr
> 3 1074034 2 2
> 7 1074034 2 1
> 11 1074034 2 2
> 15 1074034 2 9
> 19 1123003 2 2
> ------------------------------------------------------------
> y$month: 3
> suid month esr
> 4 1074034 3 2
> 8 1074034 3 1
> 12 1074034 3 2
> 16 1074034 3 9
> 20 1123003 3 2
> ------------------------------------------------------------
> y$month: 12
> suid month esr
> 1 1074034 12 6
> 5 1074034 12 1
> 9 1074034 12 2
> 13 1074034 12 9
> 17 1123003 12 2
>
> -->
>
> What I would like to do is stacking these four data frames back to one
> data frame, which in this simple example would just be y. I tried
> unlist(), unclass() and rbind(), but none of them would work.
>
>
> Thanks a lot,
>
>
>
> Stephan
>
>
>
>
>
>
>
>
>
>
> --
> -----------------------
> Stephan Lindner
> University of Michigan
>
> ______________________________________________
> 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<http://www.r-project.org/posting-guide.html>
> and provide commented, minimal, self-contained, reproducible code.
>
--
Jim Holtman
Cincinnati, OH
+1 513 646 9390
What is the problem that you are trying to solve?
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