Hi Simon,
On Wed, Jun 29, 2011 at 11:42 AM, Simon Goodman <s.j.good...@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.
The usual way to check whether an argument has been specified within a
function is by using missing().
> 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.
I'm not sure what the question is, exactly. You do something like:
myfun <- function(whatever, customlegend=TRUE) {
# name the argument, give it a default value
plot(whatever)
if(customlegend) {
# do the custom legend stuff
} else {
# do whatever the other version is
}
invisible()
}
It's all a matter of passing arguments to your functions.
If those aren't really what you were asking, then you might need to
restate the questions.
Sarah
--
Sarah Goslee
http://www.functionaldiversity.org
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