[R] Testing if a variable is specified within a function & adding TRUE/FALSE options to functions

[Gabor Grothendieck]

On Wed, Jun 29, 2011 at 11:42 AM, Simon Goodman <s.j.goodman at leeds.ac.uk> wrote:
> I have 2 related questions about functions.
>
> 1. I am writing a function to plot data from a time series with the form
>
> myplot<-function(data, d1,d2) {    }
>
> Where d1 and d2 are two dates in a time series. The idea being that if no
> values for d1 and d2 are entered then the function defaults to plotting the
> whole time series, else it plots the data for the interval specified by d1
> and d2.
>
> I am attempting to test if the variable d1 has been inputted by using a
> different function, orginally posted on a R help forum by Brian Ripley.
>
> testObject <- function(object)
> {
>   exists(as.character(substitute(object)))
> }
>
> here testObject(x) returns FALSE if x is not currently present a variable in
> the work space image.
>
> testObject works fine outside my plotting function, but not within it.... it
> always returns FALSE inside the plotting function even when d1 is being
> given by the user.
>
> I get the same result even if the testObject function is defined inside the
> plotting function....
>
> I suspect this may be due to enviroment being searched for d1.... but can't
> find work out how to make it search for d1 within the 'myplot' function - I
> think this can done using 'where' or 'environment' - but the documentation
> on these commands is a little opaque.
>
> 2. For the 'myplot' function I would also like to add a customlegend=TRUE
> (or FALSE) option, which determines if a custom legend is plotted (if not
> inputted it would default to TRUE), but haven't been able to find anything
> on how to specify this kind TRUE/FALSE of option for functions.
>

Try this:
We can just forward the first 1-3 arguments to window like this:

my.plot <- function(..., customlegend = TRUE) {
	plot(window(...))
	if (customlegend) legend("topleft", leg = "My custom legend")
}

tt <- ts(1:10)

# example 1
my.plot(tt, 3, 6)

# example 2
myplot(tt)


-- 
Statistics & Software Consulting
GKX Group, GKX Associates Inc.
tel: 1-877-GKX-GROUP
email: ggrothendieck at gmail.com