Hi Thomas,
sorry, I should have mentioned that I was using the survey package. But
thank you very much for your quick response. Your first solution worked
perfectly.
Best,
Thushyanthan
tlum...@u.washington.edu wrote:
On Mon, 2 Nov 2009, Thushyanthan Baskaran wrote:
Hi,
I am trying to write a function to compute many cross-tabulations
with the -svytable- command. Here is a simplified example of the
structure of my code (adapted from the -svytable- help file):
In the 'survey' package -- if you say what package you are using,
people don't have to guess.
data(api)
func.example<-function(variable){ dclus1<-svydesign(id=~1,
weights=~pw,data=apiclus1, fpc=~fpc)
svytable(~ variable, dclus1)
}
When I call this function with:
func.example(api99)
I get the following error:
Error in eval(expr, envir, enclos) : object 'variable' not found.
Yes, that's because you don't have a variable called 'variable' in the
design object.
(Everything works fine when I type svytable(~ api99, dclus1).)
I guess that the problem has something to do with function environments
Not really. It has to do with how formulas are evaluated. To get
substitution into a formula you need to use substitute() or bquote().
You also need to stop the argument being evaluated before it gets to
the svytable() call, and this sort of non-standard evaluation is not
recommended unless you really need it.
The easiest solution is to pass a formula, not a variable
f.example1 <- function(formula){
dclus1<-svydesign(id=~1, weights=~pw,data=apiclus1, fpc=~fpc)
svytable(formula, dclus1)
}
f.example1(~comp.imp)
The next easiest way is to pass a character string
f.example2 <- function(varname){
dclus1<-svydesign(id=~1, weights=~pw,data=apiclus1, fpc=~fpc)
formula<-make.formula(varname)
svytable(formula, dclus1)
}
f.example2("comp.imp")
The next easiest way is to pass a quoted symbol
f.example3 <- function(variable){
dclus1<-svydesign(id=~1, weights=~pw,data=apiclus1, fpc=~fpc)
eval(bquote(svytable(~.(variable), dclus1)))
}
f.example3(quote(comp.imp))
and a really ugly solution is to use non-standard evaluation to avoid
the quote()
f.example4 <- function(variable){
v<-substitute(variable)
dclus1<-svydesign(id=~1, weights=~pw,data=apiclus1, fpc=~fpc)
eval(bquote(svytable(~.(v), dclus1)))
}
f.example4(comp.imp)
There's a good reason why the survey packages uses the first style,
not the last one. Occasionally, as with subset() or with(), you need
to supply arbitrary expressions and evaluate them somewhere else than
the default location, but this sort of thing really should be avoided
if there is any alternative. It's just too hard to extend and maintain.
-thomas
Thomas Lumley Assoc. Professor, Biostatistics
tlum...@u.washington.edu University of Washington, Seattle
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