[R] using names inside a loop

[Prof Brian D Ripley]

On Thu, 24 Jan 2002, Alberto Murta wrote:

> I expected that something like
>
> > for(i in names(my.data.frame)){j <- as.name(i); print(my.data.frame$j)}
>
> should work in R (and S). There's always the possibility of using
>
> > for(i in names(my.data.frame)){print(my.data.frame[,i])}
>
> but can someone someone tell me why doesn't the 1st option work also?

Because it doesn't know that j is meant to be a variable.
What you can do is

for(i in names(my.data.frame)){
  print(eval(substitute(my.data.frame$j, list(j=i))))
}

Is there some reason to want to do this?  as.list(my.data.frame)
would seem to do the same job with some informative labels,

-- 
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)
1 South Parks Road,                     +44 1865 272860 (secr)
Oxford OX1 3TG, UK                Fax:  +44 1865 272595

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