Re: [R] legend for several graphics

From: Gavin Simpson <gavin.simpson_at_ucl.ac.uk>
Date: Wed, 05 Mar 2008 18:42:33 +0000

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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> and provide commented, minimal, self-contained, reproducible code.

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Dr. Gavin Simpson             [t] +44 (0)20 7679 0522
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