From Martin Maechler <maechler@stat.math.ethz.ch>  Tue Dec 15 17:15:11 1998
From: Martin Maechler <maechler@stat.math.ethz.ch> (Martin Maechler)
Date: Tue, 15 Dec 1998 18:15:11 +0100
Subject: legend --> buglet in plot setup  +  legend()'s S/R incompatibility
In-Reply-To: <98Dec15.104909est.13460@mailgate.bank-banque-canada.ca> (message
 from Paul Gilbert on Tue, 15 Dec 1998 10:46:10 -0500)
Message-ID: <199812151715.SAA23840@sophie.ethz.ch>

Thank you Paul; 
One could argue that it is your fault, calling  legend() without a
preceding plot in that figure.  Help says ``add legends to plots''

However, I agree
this *is* a buglet somewhere.

Look at this [which is your code ++ ]

x11()
par(mfcol = c(2, 1), mar = c(5.1, 6.1, 4.1,  2.1), ask = TRUE)
(u <- par("usr"))
for(do.box in c(FALSE,TRUE)) {
    matplot(matrix(1:30,15,2), type="l", lty=1:2)
    par(mfg = c(2, 1, 2, 1))
    print(u <- par("usr"))
    if(do.box) 
	box()
    legend(u[1:2], u[3:4], c("a","b"), lty = 1:2,  col=1:2, bty = "y")
}

##--> The first time, the legend is not properly done;
##    the second time, after "box()" it is!

---> You can use this as a workaround for the moment:

Use 
	box(col = 0)

which gives an invisible box  and makes subsequent  legend(.) work okay!

---
However, I assume you won't get what you want and what S-plus does:

S: in legend(x,y,...) , if x & y of length 2, they specify opposite CORNERS

whereas in R, they always specify just one point
we have something like 
	if(length(x) > 1) { x <- mean(x); y <- mean(y) ; ...... }
That point is determined by xjust/yjust and defaults to the left-upper corner:

In R, the size and placing of the legend's box
is determined ``automagically'', using
	x.intersp,	y.intersp,  cex   &	text.width.

Maybe we need a way to circumwent the automatic legend-box size computation...
---

Martin
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legend --> buglet in plot setup + legend()'s S/R incompatibility
Martin Maechler