I'm trying to add a legend to a ggplot
of two histograms, that may overlap and therefore would like to have them slightly transparent:
library(ggplot2)
set.seed(1)
plot.df <- data.frame(x=c(rnorm(1000,30,1),rnorm(10000,40,5)),
group=c(rep("a",1000),rep("b",10000)))
using:
ggplot(plot.df,aes(x=x,fill=factor(group)))+
geom_histogram(data=subset(plot.df,group=='a'),fill="red",alpha=0.5)+
geom_histogram(data=subset(plot.df,group=='b'),fill="darkgray",alpha=0.5)+
scale_colour_manual(name="group",values=c("red","darkgray"),labels=c("a","b"))+scale_fill_manual(name="group",values=c("red","darkgray"),labels=c("a","b"))
but all I get is:
What's missing?
Instead of plotting the two hisgrams separately, you can specify the fill
parameter in the mapping as the group
variable, in which case the legend will be automatically generated.
ggplot(plot.df, aes(x=x, fill = group)) +
geom_histogram(alpha = 0.5) +
scale_fill_manual(name="group",values=c("red","darkgray"),labels=c("a","b"))
Borrowed from here, the trick lies in setting up the fill
parameter in the mapping(i.e aes
here) of each of the histogram
plot and then you can use scale_fill_manual
normally:
ggplot(plot.df,aes(x=x))+
geom_histogram(data=subset(plot.df,group=='a'),aes(fill=group),alpha=0.5)+
geom_histogram(data=subset(plot.df,group=='b'),aes(fill=group),alpha=0.5)+
scale_fill_manual(name="group", values=c("red","darkgray"),labels=c("a","b"))
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