[R] Placing legends

[Alexander Ploner]

> > I'm trying to automate making a bunch of figures and I need a way to
> > automate legend position.  As I understand it the legend is 
> placed based 
> > on coordinates.  I don't know before hand what the 
> coordinates are going 
> > to be.  On one graph my y axis might go from -50 to -10.  
> On another it 
> > might go from 0 to 180.

I've been using the following utility - just use named arguments to
pass on to legend, i.e. "legend=", "pch=" etc.

"Legend" <- function (x="right", y="top", ..., offset=0.25)
{
# Name: Legend
# Desc: fixes a legend to one of the corners of a plot
# Auth: Alexander.Ploner at meb.ki.se

    x <- match.arg(x,c("left","center","right"))
    y <- match.arg(y,c("bottom","center","top"))
    cc <- par("usr")
    if (x=="left") {
        x  <- cc[1] + xinch(offset)
        xjust <- 0
    } else if (x=="center") {
        x  <- (cc[1] + cc[2])/2
        xjust <- 0.5
    } else if (x=="right") {
        x  <- cc[2] - xinch(offset)
        xjust <- 1
    }
    if (y=="bottom") {
        y  <- cc[3] + yinch(offset)
        yjust <- 0
    } else if (y=="center") {
        y  <- (cc[3] + cc[4])/2
        yjust <- 0.5
    } else if (y=="top") {
        y  <- cc[4] - yinch(offset)
        yjust <- 1
    }
    legend(x, y, xjust=xjust, yjust=yjust, ...)

}

HTH,

alexander

Alexander.Ploner at meb.ki.se
Phone: 46-8-524-82329
Fax  : 46-8-31 11 01
Medical Epidemiology & Biostatistics
Karolinska Institutet,
P.O. Box 281, SE-171 77 Stockholm