Question

I make several calls to mtext() using the same args:

mtext(expression(bold("Exome SNP QQ Plots")), col="black", outer=TRUE, cex=1.3)

I want to create an object containing these args, that I can pass to mtext(), rather than recreating it each time. I tried to put the args above in a variable as a list:

PageTitle <- list(expression(bold("Exome SNP QQ Plots")), col="black", outer=TRUE, cex=1.3)

And then pass the variable to mtext():

mtext(PageTitle)

This does not behave the same as calling mtext() with a complete set of args.
I suspect that mtext() is not looking for a list, but a different kind of object?

Answer 1

Function do.call is what you are looking for:

do.call(mtext, PageTitle)

We have the syntax do.call(what, args, quote = FALSE, envir = parent.frame()), here what is a function and args is a list of arguments to the function call – and that is great that you already have this list. do.call is a very useful function and it might help you in other situations too.