[R] Odp: Question about collapse/aggregate and avoidance of loops

[Petr PIKAL]

Hi

r-help-bounces at r-project.org napsal dne 29.01.2009 07:52:37:

> Dear all,
> 
> given the following data
> 
> ## original data
> id <- c(1,1,1,2,2,3)
> author <- c("A","B","C","D","E","F")
> tmp <- data.frame(id,author)
> tmp
> 
> 
>  > tmp
>    id author
> 1  1      A
> 2  1      B
> 3  1      C
> 4  2      D
> 5  2      E
> 6  3      F
> 
> What is the best (most efficient/vectorized/avoiding loops) approach to 
> obtain the following data frame?
> 
> id    author
> 1   "A, B, C"
> 2    "D, E"
> 3   "F"

Not sure if it is most efficient but

 aggregate(tmp$author, list(tmp$id), function(x) paste(x, collapse=","))

can do the trick

Regards
Petr


> 
> 
> Thanks for your help,
> 
> Bernd
> 
> 
> 
> 
> 
>  > version
>                 _
> platform       i386-pc-mingw32
> arch           i386
> os             mingw32
> system         i386, mingw32
> status         Patched
> major          2
> minor          8.1
> year           2008
> month          12
> day            22
> svn rev        47296
> language       R
> version.string R version 2.8.1 Patched (2008-12-22 r47296)
> 
> ______________________________________________
> 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.