How can I remove the legend title in ggplot2?

问题:

I have a question concerning the legend in ggplot2.

Say I have a hypothetical dataset about mean carrot length for two different colours at two farms:

carrots<-NULL
carrots$Farm<-rep(c("X","Y"),2)
carrots$Type<-rep(c("Orange","Purple"),each=2)
carrots$MeanLength<-c(10,6,4,2)
carrots<-data.frame(carrots)

I make a simple bar plot:

require(ggplot2)
p<-ggplot(carrots,aes(y=MeanLength,x=Farm,fill=Type)) + 
geom_bar(position="dodge") +
opts(legend.position="top")
p

My question is: is there a way to remove the title ('Type') from the legend?

Thanks!

回答1:

You can modify the legend title by passing it as the first parameter to a scale. For example:

ggplot(carrots, aes(y=MeanLength, x=Farm, fill=Type)) + 
  geom_bar(position="dodge") +
  theme(legend.position="top", legend.direction="horizontal") +
  scale_fill_discrete("")

There is also a shortcut for this, i.e. labs(fill="")

Since your legend is at the top of the chart, you may also wish to modify the legend orientation. You can do this using opts(legend.direction="horizontal").

回答2:

I found that the best option is to use + theme(legend.title = element_blank()) as user "gkcn" noted.

For me (on 03/26/15) using the previously suggested labs(fill="") and scale_fill_discrete("") remove one title, only to add in another legend, which is not useful.

回答3:

You can use labs:

p + labs(fill="")

回答4:

The only way worked for me was using legend.title = theme_blank() and I think it is the most convenient variant in comparison to labs(fill="") and scale_fill_discrete(""), which also could be useful in some cases.

ggplot(carrots,aes(y=MeanLength,x=Farm,fill=Type)) + 
geom_bar(position="dodge") +
opts(
    legend.position="top",
    legend.direction="horizontal",
    legend.title = theme_blank()
)

P.S. There are more useful options in documentation.

回答5:

You've got two good options already, so here's another using scale_fill_manual(). Note this also lets you specify the colors of the bars easily:

ggplot(carrots,aes(y=MeanLength,x=Farm,fill=Type)) + 
  geom_bar(position="dodge") +
  opts(legend.position="top") +
  scale_fill_manual(name = "", values = c("Orange" = "orange", "Purple" = "purple"))

If you are using the up-to-date (As of January 2015) version of ggplot2 (version 1.0), then the following should work:

ggplot(carrots, aes(y = MeanLength, x = Farm, fill = Type)) +
  geom_bar(stat = "identity", position = "dodge") +
  theme(legend.position="top") +
  scale_fill_manual(name = "", values = c("Orange" = "orange", "Purple" = "purple"))