Getting a legend with two layers

[Forafo San]

I have annual time-series data on the U.S. federal government's
receipts and outlays. I'm displaying the series on the same plot, one
as geom_area and the other as geom_line. The resulting plot looks very
nice. However, I'm not sure how to get a legend with two boxes one
with the whole box filled with the fill colour of the layer created
with geom_area and the other box containing a line of the size and the
colour that appear in the layer created with geom_line.

Any help is appreciated.
-Premal P. Vora

FYI the code:
---------------------------------
p<-ggplot(dat,aes(year,outlays))
p<- p + geom_area(fill="red")
p + geom_line(aes(y=receipts),size=1)

[fernando]

Hi Premal,

I think one option is to restructure your data with melt and use then manual
scales.

Hope this helps,
fernando

dat <- data.frame(year = 1901:2000, outlays = rnorm(100), receipts =
rnorm(100))
dat <- melt(dat, id.vars = "year")
str(dat)
names(dat) <- c("year", "ind", "series")

p <- ggplot(dat, aes(x = year, y = series)) +
geom_area(aes(fill = ind)) +
geom_line(aes(colour = ind), size = I(1)) +
scale_fill_manual(name = "The same legend title", values =
c("outlays" = "red", "receipts" = NA)) +
scale_colour_manual(name = "The same legend title", values =
c("outlays" = NA, "receipts" = "blue"))
p

sessionInfo()
R version 2.11.1 (2010-05-31)
x86_64-pc-mingw32

locale:
[1] LC_COLLATE=Spanish_Spain.1252 LC_CTYPE=Spanish_Spain.1252
[3] LC_MONETARY=Spanish_Spain.1252 LC_NUMERIC=C
[5] LC_TIME=Spanish_Spain.1252

attached base packages:
[1] grid stats graphics grDevices utils datasets methods
[8] base

other attached packages:
[1] ggplot2_0.8.8 proto_0.3-8 reshape_0.8.3 plyr_1.1
foreign_0.8-40

loaded via a namespace (and not attached):
[1] digest_0.4.2 tools_2.11.1

-----Mensaje original-----
De: ggp...@googlegroups.com [mailto:ggp...@googlegroups.com] En nombre de
Forafo San
Enviado el: martes, 03 de agosto de 2010 16:47
Para: ggp...@googlegroups.com
Asunto: Getting a legend with two layers

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[Forafo San]

Fernando,
Your code works perfectly and I understand most of it except: in the
geom_area and the geom_line syntax that you wrote, how does ggplot
figure out that the area layer should plot only one series (and not
the other) and the line syntax should plot the other series (and not
the first). It's probably somewhere in Hadley's ggplot2 book, but if
you can provide a quick insight or reference, that would be immensely
helpful.

Thanks a lot.
-Premal

[fernando]

Hi Forafo,

If you run the example line by line, you will note that indeed both
geom_area and geom_line produce the expected output, e.g. areas and lines
with different fills and colours for each level of the factor. The trick is
indeed in the manual scales, in which you can specify how each level will be
draw; by setting alternatively the fill or the colour to NA, you obtain the
desired effect of drawing only one of the geoms for each level of the
factor. Because you use the same 'name' for both scales, they are combined.

Hope this helps,
fernando

-----Mensaje original-----
De: Forafo San [mailto:ppv....@gmail.com]
Enviado el: miércoles, 04 de agosto de 2010 18:11
Para: fernando
CC: ggp...@googlegroups.com
Asunto: Re: Getting a legend with two layers