[R] aggregate and names of factors

[Peter Dalgaard]

Christophe Pallier <pallier at lscp.ehess.fr> writes:

> Hello,
> 
> I use the function 'aggregate' a lot.
> 
> One small annoyance is that it is necessary to name the factors in the
> 'by' list to get the names in the resulting data.frame (else, they
> appear as Group.1, Group.2...etc). For example, I am forced to
> write:
> 
> aggregate(y,list(f1=f1,f2=f2),mean)
> 
> instead of aggregate(y,list(f1,f2),mean)
> 
> (for two factors with short names, it is not such a big deal, but I
> ususally have about 8 factors with long names...)
> 
> I wrote a modified 'aggregate.data.frame' function (see the code
> below) so that it parses the names of the factors and uses them in the
> output
> data.frame. I can now typer aggregate(y,list(f1,f2),mean) ans the
> resulting data.frame
> has variables with names 'f1' and 'f2'.
> 
> However, I have a few questions:
> 
> 1. Is is a good idea at all? When expressions rather than variables are
>    used as factors, this will probably result in a mess. Can one test
>    if an argument within a list, is just a variable name or a more
>    complex expression?). Is there a better way?

This issue is not just relevant for aggregate. There are a couple of
other places where you want a named list to get names on output -
lapply(list(foo,bar,baz) function(x) lm(x~age)), say. One option that
I've been toying around with is to clone the code from data.frame and
have a function namedList() or nlist() which automagically supplies
names by deparsing the call. Now where did I put that code sketch...

-- 
   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