[R] Using functions within functions (environment problems)

[Colin Beale]

Hi everyone,

I've been having difficulty writing wrapper functions for some
functions where those same functions include other functions with
eval()
calls where the environment is specified. A very simple example using
function lmer from lme4:

lmerWrapper <- function(formula, data, family = gaussian, method =
c("REML", 
    "ML", "PQL", "Laplace", "AGQ"), control = list(), start = NULL, 
    subset, weights, na.action, offset, contrasts = NULL, model =
TRUE,

    ...)
{

    xNew <- runif(0,1, length(data[,1]))
    fNew <- sample(1:4, length(data[,1]), replace = T)
    data <- as.data.frame(cbind(data, xNew, fNew))
    formula <- update(formula, .~. + xNew + (1|fNew))
    out <- lmer (formula = formula, data = data, family = family,
method =
        method, weights = weights, control = control, start = start,
        subset = subset, na.action = na.action, offset = offset,
        contrasts = contrasts, model = model)
}

dat <- data.frame(Y = rnorm(100), X1 = rnorm(100), X2 = rnorm(100), 
        F1 = as.factor(sample(1:4, 400, replace = T)))
test <- lmerWrapper (Y ~ X1 + X2 + (1|F1), data = dat)


This function attempts to create two new variables, add these to the
data.frame and modify the formula for include these two new variables,
and then fit this expanded model using lmer. Clearly the example is
silly, but it illustrates the problem as it fails with the error:

Error in eval(expr, envir, enclos) : object "xNew" not found

because a function within lmer (lmerFrames) makes an eval call where
the environment is specified as the .GlobalEnv which doesn't contain
xNew - it needs to be looking in the environment from which it was
called rather than going right back to the root. In a more general
context, I might like to create a function where I don't specify a new
data.frame in the wrapper, but want the function to search the back
down
the search path for each component, finding xNew in the environment of
the wrapper function and X1 in the .GlobalEnv. Is there a general
solution to this? Or do I need to create a modified lmer function that
calls a modified lmerFrames function where I specify the environment
differently? There's quite a lot in the archives dealing with
environments and search paths, but I'm either not understanding how to
apply the wisdom therein, or not finding the specific answer to my
problem, and I should say that I have this problem with more than just
the lmer function.

Thanks for any pointers,

Colin

> sessionInfo()
R version 2.4.1 (2006-12-18) 
i386-pc-mingw32 

locale:
LC_COLLATE=English_United Kingdom.1252;LC_CTYPE=English_United
Kingdom.1252;LC_MONETARY=English_United
Kingdom.1252;LC_NUMERIC=C;LC_TIME=English_United Kingdom.1252

attached base packages:
[1] "stats"     "graphics"  "grDevices" "datasets"  "tcltk"    
"utils"
    "methods"   "base"     

other attached packages:
      debug    mvbutils        lme4      Matrix     lattice   
svSocket
       svIO      R2HTML      svMisc       svIDE 
    "1.1.0"     "1.1.1" "0.9975-10"  "0.9975-8"   "0.14-16"    
"0.9-5"
    "0.9-5"      "1.58"     "0.9-5"     "0.9-5" 




Dr. Colin Beale
Spatial Ecologist
The Macaulay Institute
Craigiebuckler
Aberdeen
AB15 8QH
UK

Tel: 01224 498245 ext. 2427
Fax: 01224 311556
Email: c.beale at macaulay.ac.uk 



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