R devel - Dec 1998 - legend

I am trying to put a legend below some plots as follows:

 x11()
 par(mfcol = c(2, 1), mar = c(5.1, 6.1, 4.1,  2.1))
 matplot(matrix(1:30,15,2), type="l", lty=1:2)
 par(mfg = c(2, 1, 2, 1))
 legend((par()$usr)[1:2], (par()$usr)[3:4], c("a","b"), lty
= 1:2,  col=1:2, bty
= "y")

The letters "a" and "b" print but not the lines. If I omit
par(mfg = c(2, 1, 2,
1)) then the
legend prints properly but on top of the plot in the first area.

Paul Gilbert


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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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