how to add default elements to `...` when passing those arguments on to another function

Question

here's a minimal reproducible example of what i want to happen

myfun <- 
    function( ... ){

        # myfun only passes `...` on to the plot function
        plot( 
            ... ,
            if( !'xlab' %in% names( list( ... ) ) ) xlab = 'mylabel' ,
            if( !'ylab' %in% names( list( ... ) ) ) ylab = 'ylabel' 
        )
    }

# works the way i want: user specified `xlab` and `ylab` so `...` used them
myfun( 1 , 1 , xlab = "new label" , ylab = "another label" )

# fails
myfun( 1 , 1 )
# Error in plot.window(...) : invalid 'xlim' value

since the user did not specify xlab and ylab, i wanted my function to use the defaults that i have set. so

plot( 1 , 1 , xlab = 'mylabel' , ylab = 'ylabel' )

what's the smartest way to do this if i have many possibilities like xlab and ylab? i might want add defaults for title= and xlim= and ylim= as well, so writing out every combination is not feasible? thanks!!

Answer 1

Solution 1

Make your own custom wrapper to the plot function:

myplot <- function(x, y, xlab = 'mylabel', ylab = 'ylabel', ...){
  plot(x, y, xlab = xlab, ylab = ylab, ...)
}


myfun <- 
  function( ... ){

    # myfun only passes `...` on to the plot function
    myplot(...)

  }

Now the following calls work as I think you want them to work:

myfun(1, 1)
myfun(1, 1,xlab = "new label" , ylab = "another label" )

Solution 2

You can also use list(...) and do.call in the following manner:

myfun <- 
  function( ... ){

    dots = list(...)

    # check whether needed defaults are supplied, if not, supply them.
    if ~grep('xlab', names(dots) ){
      dots$xlab = 'mylabel'
    }        
    if ~grep('ylab', names(dots) ){
      dots$ylab = 'ylabel'
    }


    # myfun only passes `...` on to the plot function
    do.call(plot, dots)

  }