Below is an example of a problem I encounter repeatedly when I write
functions. A call works at the command line, but it does not work inside a
function, even when I have made sure that all required variables are
available within the function. The only way I know to solve it is to make
the required variable global, which of course is dangerous. What is the
elegant or appropriate way to solve this?
# The call to ns works at the command line:
> junk<-ns(DAT$Age, knots=74)
# The call to lmer works at the command line, with the call to ns nested
within it:
> junk2<-lmer(formula=Finished ~ Sex01 + ns(DAT$Age, knots= 74 ) + MinCC +
PzC + (1 | NAME ) + (1 | Year), data=myDATonly, family="binomial")
But now I want to do this within a function such as the following:
> myfn
function(myknot=74) {
library(lme4)
library(splines)
cat("myknot=", myknot, "\n")
myMER<-lmer(formula=Finished ~ Sex01 + ns(DAT$Age, knots= myknot) +
MinCC + PzC + (1 | NAME ) + (1 | Year), data=myDATonly, family="binomial")
}
> myfn(74)
myknot= 74
Error in ns(DAT$Age, knots = myknot) : object "myknot" not found
# The bad way to do it: revise myfn to make myknot a global variable:
> myfn
function(myknot=74) {
library(lme4)
library(splines)
cat("myknot=", myknot, "\n")
myknot<<-myknot
myMER<-lmer(formula=Finished ~ Sex01 + ns(DAT$Age, knots= myknot
) + MinCC + PzC + (1 | NAME ) + (1 | Year), data=myDATonly,
family="binomial")
}
> z<-myfn(74)
myknot= 74
# Runs fine but puts a global variable into .GlobalEnv.
> sessionInfo()
R version 2.6.2 (2008-02-08)
i386-pc-mingw32
locale:
LC_COLLATE=English_United States.1252;LC_CTYPE=English_United
States.1252;LC_MONETARY=English_United
States.1252;LC_NUMERIC=C;LC_TIME=English_United States.1252
attached base packages:
[1] splines stats graphics grDevices datasets utils methods
base
other attached packages:
[1] lme4_0.999375-13 Matrix_0.999375-9 lattice_0.17-6
loaded via a namespace (and not attached):
[1] boot_1.2-32 grid_2.6.2
>
Thanks for any insight.
Jacob A. Wegelin
[EMAIL PROTECTED]
Assistant Professor
Department of Biostatistics
Virginia Commonwealth University
730 East Broad Street Room 3006
P. O. Box 980032
Richmond VA 23298-0032
U.S.A.
http://www.people.vcu.edu/~jwegelin
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