[R] adding a legend to the plot (but outside of it)

[Dimitri Liakhovitski]

Hello!

My code below creates a data frame and a plot for it.
However, I can't figure out how to add a legend that is not ON the
plot itself, but outside of it (e.g., to the right of my graph or
below it). I tried something: I put a line par(xpd=T,
mar=par()$mar+c(0,0,0,4)) right before my plot command), but that
screwed up all my gridlines - they covered all graph and do not
coincide with tickmarks anymore.
Any help would be greatly appreciated!
Dimitri



my.data<-data.frame(date=c(20080301,20080401,20080501,20080601,20080701,20080801,20080901,20081001,20081101,20081201,20090101,20090201,20090301,20090401,20090501,20090601,20090701,20090801,20090901,20091001,20091101,20091201,20100101,20100201,20100301,20100402,20100503),
x=c(1.1, 1, 1.6, 1, 2, 1.5, 2.1, 1.3, 1.9, 1.1, 1, 1.6, 1, 2, 1.5,
2.1, 1.3, 1.9, 1.1, 1, 1.6, 1, 2, 1.5, 2.1, 1.3, 1.9),
y=c(-4,-3,-6,-5,-7,-5.2,-6,-4,-4.9,-4,-3,-6,-5,-7,-5.2,-6,-4,-4.9,-4,-3,-6,-5,-7,-5.2,-6,-4,-4.9),
z=c(-0.2,-0.3,-0.4,-0.1,-0.2,-0.05,-0.2,-0.15,-0.06,-0.2,-0.3,-0.4,-0.1,-0.2,-0.05,-0.2,-0.15,-0.06,-0.06,-0.2,-0.3,-0.4,-0.1,-0.2,-0.05,-0.2,-0.15),
a=c(10,13,15,15,16,17,15,16,14,10,13,15,15,16,17,15,16,14,10,13,15,15,16,17,15,16,14))
my.data$date<-as.character(my.data$date)
my.data$date<-as.Date(my.data$date,"%Y%m%d")
(my.data)
str(my.data)

positives<-which(colSums(my.data[2:ncol(my.data)])>0) # which vars
have positive column sums?
negatives<-which(colSums(my.data[2:ncol(my.data)])<0) # which vars
have negative column sums?

y.max<-1.1*max(rowSums(my.data[names(positives)])) # the max on the y
axis of the chart
y.min<-1.1*min(rowSums(my.data[names(negatives)])) # the min on the y
axis of the chart
ylim <- c(y.min, y.max)
order.positives<-rev(rank(positives))
order.of.pos.vars<-names(order.positives)
order.negatives<-rev(rank(negatives))
order.of.neg.vars<-names(order.negatives)
order<-c(order.negatives,order.positives)
order.of.vars<-names(order)   # the order of variables on the chart -
from the bottom up
### so, the bottom-most area should be for z, the second from the
bottom area- for y (above z)

all.colors<-c('red','blue','green','orange','yellow','purple')
xx <- c(my.data$date, rev(my.data$date))
bottom.y.coordinates<-rowSums(my.data[names(negatives)])

plot(x=my.data$date, y=bottom.y.coordinates, ylim=ylim, col='white',
type='l', xaxt='n',
	ylab='Title for Y', xlab="", main='Chart Title')

for(var in order.of.neg.vars){
	top.line.coords<-bottom.y.coordinates-my.data[[var]]
	bottom.coords<-c(bottom.y.coordinates,rev(top.line.coords))
	polygon(xx,bottom.coords,col=all.colors[which(names(my.data) %in% var)])
	bottom.y.coordinates<-top.line.coords
}

for(var in order.of.pos.vars){
	top.line.coords<-bottom.y.coordinates+my.data[[var]]
	bottom.coords<-c(bottom.y.coordinates,rev(top.line.coords))
	polygon(xx,bottom.coords,col=all.colors[which(names(my.data) %in% var)])
	bottom.y.coordinates<-top.line.coords
}

axis(1, labels =format(as.Date(my.data$date, origin="1970-01-01"),
"%Y-%m-%d"), at=my.data$date, las=2,cex.axis=0.7)
grid(nx=(length(my.data$date)-1),ny=NULL,col = "lightgray", lty =
"dotted",lwd = par("lwd"))

-- 
Dimitri Liakhovitski
Ninah Consulting
www.ninah.com