[R] Is there a "by()" function in R like in S?

[Peter Dalgaard BSA]

Sven Garbade <garbade at mip.paed.uni-muenchen.de> writes:

>   > by(data, year, summary)
> 
> where "data" is a matrix containing the variable "year". After grouping
> the matrix to variable "year", the function "summary" is applied to each
> group.

It's not in there, but it shouldn't be too hard to write one. Here's
a start:

by <- function(data, INDICES, FUN, ...)
{
   ee <- substitute(tapply(1:nrow(data), INDICES, FUNx))
   FUNx <- function(x) FUN(data[x,], ...)
   ans <- eval(ee, data)
   class(ans)<-"by"
} 

Now go and write print.by ...

-- 
   O__  ---- Peter Dalgaard             Blegdamsvej 3  
  c/ /'_ --- Dept. of Biostatistics     2200 Cph. N   
 (*) \(*) -- University of Copenhagen   Denmark      Ph: (+45) 35327918
~~~~~~~~~~ - (p.dalgaard at biostat.ku.dk)             FAX: (+45) 35327907
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