[R] legend for several graphics

[Gavin Simpson]

On Wed, 2008-03-05 at 15:28 +0100, Georg Otto wrote:
> Hi,
> 
> I am trying to generate a figure of 9 plots that are contained in one
> device by using
> 
> par(mfrow = c(3,3,))
> 
> I would like to have 1 common legend for all 9 plots somewhere outside
> of the plotting area (as opposed to one legend inside each of the 9
> plots, which the function legend() seems to generate by default).
> 
> Any hint how to do this?

Here's one way:

op <- par(mfrow = c(3,3), ## split region
          oma = c(5,0,4,0) + 0.1, ## create outer margin
          mar = c(5,4,2,2) + 0.1) ## shrink some margins
plot(1:10, main = "a", pch = 1:2, col= 1:2)
plot(1:10, main = "b", pch = 1:2, col= 1:2)
plot(1:10, main = "c", pch = 1:2, col= 1:2)
plot(1:10, main = "d", pch = 1:2, col= 1:2)
plot(1:10, main = "e", pch = 1:2, col= 1:2)
plot(1:10, main = "f", pch = 1:2, col= 1:2)
plot(1:10, main = "g", pch = 1:2, col= 1:2)
plot(1:10, main = "h", pch = 1:2, col= 1:2)
plot(1:10, main = "i", pch = 1:2, col= 1:2)
## title
mtext("My Plots", side = 3, outer = TRUE, font = 2, line = 1, cex = 1.2)
## draw legend
legend(-12.5, -6, legend = c("Type 1", "Type 2"), pch = 1:2, col = 1:2,
ncol = 2)
par(op)

I had to fiddle by hand with the legend x and y locations to get it
roughly centred. There has to be better way - probably something to do
with reseting the plot region, but I can't recall how to do that now. If
there is, I'm sure someone will tell me what I overlooked.

Is this what you were looking for?

G

> 
> Best,
> 
> Georg
> 
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