Question

Yesterday, I asked a question regarding how to plot multiple (horizontal-ish) lines, each with a user-specified color, without using a loop.

I tried to use the suggested function matplot() to plot the short vertical lines shown in the plot below with the relevant code.

    ci = matrix(1:30, nrow=3, byrow=T)
    ci=list(rbind(ci[1,], ci[1,]+2),
            rbind(ci[2,], ci[2,]+2),
            rbind(ci[3,], ci[3,]+2))
    x = rbind(1:10, 1:10)
    plot(-5, xlim=c(1,10), ylim=c(1,32)) 
    invisible(mapply(matlines, x=list(x), y=ci, 
              col=c("red","blue","black"), 
              lty = 1))

This is all good. However, I am trying to wrap this code inside a function, and I would like to be able to input a list of optional arguments, which can then be passed to mapply/matlines. I tried to use the argument MoreArgs in mapply() to no avail. It seems that arguments that MoreArgs takes are not treated the same as others. As you can see in the first code, each item of the list gets a different color, but when I put col inside the list args.ci, the 3 colors are recycled within each item of the list. I wonder if there is anyway to resolve this issue so that if I have multiple values for an argument, each value gets applied to one item of a list. Thanks!

    args.ci = list(col=c("red","blue","black"), lty=1:3)
    plot(-5, xlim=c(1,10), ylim=c(1,32)) 
    invisible(mapply(matlines, x=list(x), y=ci, 
              MoreArgs = args.ci))

Answer 1

Here’s a general approach to this sort of problem. You should be able to adapt it to do more exactly what you want:

myFun <- function(...) {
    fixedArgs <- list(matlines, x=list(x), y=ci)
    dots <- list(...)
    allArgs <- c(fixedArgs, dots)
    plot(-5, xlim=c(1,10), ylim=c(1,32)) 
    invisible(do.call(mapply, allArgs))
}

myFun(col=c("red","blue","black"), lty=1)