In your test function there is no lexically visible definition for the
`colnum` variable used in defining main, so that error is what you
expect from lexical scoping. Lazy evaluation dictates when (and if)
the `main` argument is evaluated, but the environment in which it is
evaluated is determined by the context where the expression is written
in the code, i.e. within the function mmatplotTest.
The error you get when you take out the `main` is coming from `subset`
and is due to the fact that subset is one of those functions that uses
non-standard evaluation for some of its arguments, in this case
`select`. This makes it (slightly) easier to use at intereactive top
level but much more complicated to use within a function. The key in
reading the help page for `subset` is that the argument `select`
should be an expression (actually the literal argument expression is
used, which in this case is the expression consisting of the single
variable `colnum` and is not useful here). You need to use another
function in your sapply call, something like
function(d) d[,colnum]
may do.
Best,
luke
On Sun, 4 Mar 2007, Thaden, John J wrote:
Apparently you're right that colnum doesn't exist when it needs to
be evaluated, but why? Why is 'paste' being evaluated so early? It is,
after all, the value of an argument ('main') of my mmatplot function
with colnum being another argument. I thought arguments were lazy-loaded.
Does using mapply change the rules?
Is there a way (like mapply) to loop at some lower level rather than
Explicitly, in the R script, as in your suggestion? For speed's sake?
Thanks. -John
On Sunday Mar 4 2007, jim holtman <[EMAIL PROTECTED]> replied
First of all, 'colnum' does not exist when the 'paste' is called.
This probably does what you want:
for (colnum in 1:ncol(A)){
mmatplot(colnum, 1:nrow(A), A, main=paste("Array input, column",
colnum))
}
On 3/4/07, John Thaden <[EMAIL PROTECTED]> wrote:
Hello, the code below is supposed to be a wrapper for matplot to
do columnwise visible comparison of several matrices, but I'm
doing something wrong because I can't access an argument called
'colnum'. I'd be most grateful for some insight.
Thanks,
John
Little Rock, AR
################################
# mmatplot is a matplot wrapper to compare the same column of
# several matrices. Arg y is either a list of matrices with
# equal number of rows, or an array. The scalar n gives the
# column of each matrix or array slab to plot. par values and
# matplot args are accepted, e.g., ylog. mmatplot is intended
# to be mapply-compatible to test multiple columns.
mmatplot <- function(colnum, x, y, ...){
switch(class(y),
array = y <- y[, colnum, ],
list = y <- sapply(X = y, FUN = subset, select = colnum))
stopifnot(is.matrix(y))
matplot(x, y, ...)
}
#This is just a tester function
mmatplotTest <- function(){
oldmf <- par("mfrow")
par(mfrow = c(2,3))
A <- array(data = rnorm(90), dim = c(10, 3, 3))
L <- list(A[, , 1], A[, , 2], A[, , 3])
# The 'main' argument below throws the error, but if
# commented out, another error crops up due to 'colnum'.
# Test with class(y) == "array"
mapply(X = 1:ncol(A), FUN = mmatplot, x = 1:nrow(A), y = A,
main = paste("Array input, column", colnum))
# Test with class(y) == "list"
mapply(1:ncol(L[[1]]), mmatplot, x = 1:nrow(L[[1]]), y = L,
main = paste("List input, column", colnum))
par(mfrow = oldmf)
}
#Run the test
mmatplotTest()
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