Writing ggplot functions in R with optional arguments

Question

I have a series of ggplot graphs that I\'m repeating with a few small variations. I would like to wrap these qplots with their options into a function to avoid a lot of repetiti

Answer 1

Note that you can also use missing(facets) to check if the facets argument was specified or not. If you use @JD Long's solution, it would look something like this:

qhist <- function(variable, df, heading, facets) {
  ... insert @JD Longs' solution ...

  if (!missing(facets)) d <- d + facet_wrap(as.formula(paste("~", facets)))
  return(d)
}

...Note that I also changed the default argument from facets=NULL to just facets.

Many R functions use missing arguments like this, but in general I tend to prefer @JD Long's variant of using a default argument value (like NULL or NA) when possible. But sometimes there is no good default value...

Answer 2

Probably, the best way is to stop using such unusual variable names including commas or spaces.

As a workaround, here is an extension of @JDLong's answer. The trick is to rename the facet variable.

f <- function(dat, facet = NULL) {
    if(!missing(facet)) {
        names(dat)[which(names(dat) == facet)] <- ".facet."
        ff <- facet_wrap(~.facet.)
    } else {
        ff <- list()
    }
    qplot(x, y, data = dat) + ff
}

d <- data.frame(x = 1:10, y = 1:10, "o,o" = gl(2,5), check.names=F)

f(d, "o,o")
f(d)

Answer 3

the way to set up a default is like this:

testFunction <- function( requiredParam, optionalParam=TRUE, alsoOptional=123 ) {
  print(requiredParam)
  if (optionalParam==TRUE) print("you kept the default for optionalParam")
  paste("for alsoOptional you entered", alsoOptional)
}

*EDIT*

Oh, ok... so I think I have a better idea of what you are asking. It looks like you're not sure how to bring the optional facet into the ggplot object. How about this:

  qhist <- function(variable, df, heading, facets=NULL) {
  d <- qplot(variable, data = df, geom = "histogram", binwidth = 2000, 
        xlab = "Salary", ylab = "Noms") + 
  theme_bw() +
  scale_x_continuous(limits=c(40000,250000), 
             breaks=c(50000,100000,150000,200000,250000), 
             labels=c("50k","100k","150k","200k","250k")) +
  opts(title = heading, plot.title = theme_text(face = "bold", 
       size = 14), strip.text.x = theme_text(size = 10, face = 'bold')) 
  # If facets argument supplied add the following, else do not add this code
  if (is.null(facets)==FALSE) d <- d + facet_wrap(as.formula(paste("~", facets)))
  d
  return(d)
  }

I have not tested this code at all. But the general idea is that the facet_wrap expects a formula, so if the facets are passed as a character string you can build a formula with as.formula() and then add it to the plot object.

If I were doing it, I would have the function accept an optional facet formula and then pass that facet formula directly into the facet_wrap. That would negate the need for the as.formula() call to convert the text into a formula.