Fw: [R] eval and as.symbol question

[Peter Dalgaard BSA]

"Gary Collins" <gco at eortc.be> writes:


> >
> > You might try something like this instead:
> >
> > apply(df, 2, function(x) sum(is.na(x)))
> >
> >
> >
> > Hope this helps
> >
> > Kaspar
> 
> I want to avoid this. I know how the apply function works. The counting
> missing items was merely an example, there are a number of ways to solve
> that particular problem. My question is how to use as.symbol, eval and paste
> to get the required result as I will use very similar steps.

You should probably reconsider the hint from Kaspar that you might
want a more structured solution. Manipulation of code via text strings
is usually not The Right Way of doing things. 

However, if you must, you need to notice that as.symbol creates a
symbol from *any* textstring

> "]{" <- 5
> eval(as.symbol( "]{"))
[1] 5

However a$b is usually not a single symbol but three, an indexing
expression consisting of a, $, and b. If you want to get that from a
text string you need parse("a$b").

-- 
   O__  ---- Peter Dalgaard             Blegdamsvej 3  
  c/ /'_ --- Dept. of Biostatistics     2200 Cph. N   
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