[R] passing a variable (containing the value of the argument) to a function
Peter Dalgaard
p.dalgaard at biostat.ku.dk
Wed Oct 22 22:35:44 CEST 2003
Spencer Graves <spencer.graves at pdf.com> writes:
> Hi, Peter: How does that compare with the following: for (myname
> in names(myframe)[1:4]){
> mdl <- formula(paste(myname, "~ etc.etc"))
> myfit <- lm(mdl, data=myframe)
> print(summary(myfit))
> }
>
> Or: for (myname in names(myframe)[1:4]){
> lm.txt <- paste("lm(", myname, "~ etc.etc, data=myframe)")
> myfit <- eval(parse(text=lm.txt))
> print(summary(myfit))
> }
>
> You are teaching me new uses of "substitute", and I just wonder
> about the relative advantages and disadvantages of the different
> approaches. Thanks,
> spencer graves
Those variants should work (and similar code is all over the place in
the modelling functions). I just tend to prefer to avoid going via the
textual representation. There are a couple of devils lurking in there,
in particular if a data frame has variables with "funny names" -
spaces or special characters inside, for example.
To wit:
> myname <- "foo bar"
> lm.txt <- paste("lm(", myname, "~ etc.etc, data=myframe)")
> lm.txt
[1] "lm( foo bar ~ etc.etc, data=myframe)"
> parse(text=lm.txt)
Error in parse(file, n, text, prompt) : parse error
--
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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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