Simple question, I hope. I want to write a plotting function that has a default value for the y-axis label if the user doesn't specify. I'd also like to allow the ...
argument for other plotting parameters, and allow the user to set ylab
manually. But I can't figure out how to do this.
# simple scatterplot function with a default ylab
scatter <- function(x,y, ...) {
plot(x, y, ylab="Default y-axis label", ...)
}
# generate data
x <- rnorm(100)
y <- x+rnorm(100)
# use the default
scatter(x,y)
# here I want to use my own label, but I get an error!
scatter(x, y, ylab="New y-axis label")
The error I get is:
Error in plot.default(x, y, ylab = "Default y-axis label", ...) :
formal argument "ylab" matched by multiple actual arguments
I understand the problem, but I don't know the best way to fix it. Thanks for the help!
EDIT: I realize I can do something like
scatter <- function(x,y,ylab = "Default y-axis label", ...) {
plot(x, y, ylab= ylab, ...)
}
...but if I'm writing a package to submit to CRAN, and I have lots of default options I'd like to fiddle with, I don't want to have to document all these standard plotting arguments because they're used in my function definition.
Try doing this instead:
scatter <- function(x,y,ylab = "Default y-axis label", ...) {
plot(x, y, ylab= ylab, ...)
}
Expanding slightly on Arun's answer, this is a sketch of one route to take if you have many arguments:
def_args <- list(ylab = "Default Label",xlab = "Default Label")
scatter <- function(x,y, ...) {
cl <- as.list(match.call())[-1L]
do.call("plot",c(cl,def_args[!names(def_args) %in% names(cl)]))
}
Some thought would be needed to decide how you want to handle partial matching of arguments (if at all). e.g. perhaps something like this:
scatter <- function(x,y, ...) {
cl <- as.list(match.call())[-1L]
names(cl) <- match.arg(names(cl),
names(formals(plot.default)),several.ok = TRUE)
do.call("plot",c(cl,def_args[!names(def_args) %in% names(cl)]))
}
would handle partial matching of arguments.
One way using match.call
to check if ylab
has been specified as an argument:
scatter <- function(x,y, ...) {
mcall = as.list(match.call())[-1L]
if (!"ylab" %in% names(mcall))
plot(x, y, ylab="Default y-axis label", ...)
else plot(x, y, ...)
}
As mentioned under comment list(...)
is a nicer way to get just the dots argument expanded than having to get all the formal arguments with match.call
.
You might also try using pmatch
instead of %in%
for partial matching of arguments.
I use a function to build an argument list. In my case, I do not care about partially matching argument names, which is good because this won't support it.
# Create a list of input arguments.
# Allow arguments to be specified multiple times, first definition wins.
# The resulting list is intended to be passed to do.call().
make.args <- function(..., PRE.ARGS=list(), POST.ARGS=list()) {
a <- list()
l <- c(PRE.ARGS, list(...), POST.ARGS)
for (name in unique(names(l))) {
a[[name]] <- l[[name]] # First occurrence will be found.
}
return(a)
}
An example of its use:
plot.rate <- function(col, cond=NULL, ...) {
col <- paste(col, collapse=' + ')
f <- paste(col, '~ Rate')
if (!is.null(cond)) {
cond <- paste(cond, collapse=' + ')
f <- paste(f, cond, sep='|')
}
arg.list <- make.args(...
, x = as.formula(f)
, main=col
, grid=TRUE
, scales=list(x=list(alternating=1) # bottom(/left)
, y=list(alternating=3)) # both
, xlab='x RTM'
)
do.call(xyplot, arg.list)
}
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