ggplot legend key color and items

问题

Using the following data frame:

sdf<-data.frame(hours=gl(n=3,k=1,length=9,labels=c(0,2,4)),    
                count=c(4500,1500,2600,4000,800,200,1500,50,20),
                machine=gl(n=3,k=3,length=9,labels=c("A","B","C")))

The following graph can be produced using either of these scripts:

ggplot(data=sdf,aes(x=hours,y=count,group=machine,fill=machine))+
  geom_area(data=sdf[sdf$machine=="A",])+
  geom_area(data=sdf[sdf$machine=="B",])+
  geom_area(data=sdf[sdf$machine=="C",])

ggplot(data=sdf,aes(x=hours,y=count,group=machine,fill=machine))+
  geom_area(position="dodge")

However, when the fill color is changed, the item in the legend disappears.

ggplot(data=sdf,aes(x=hours,y=count,group=machine,fill=machine))+
  geom_area(data=sdf[sdf$machine=="A",])+
  geom_area(data=sdf[sdf$machine=="B",],fill="darkorchid")+
  geom_area(data=sdf[sdf$machine=="C",])

Ideally, the legend should show the color change.

Question: What script can create items in a legend as well as offer color controls for those items?

回答1:

You can adjust the values assigned to any aesthetic using scale_X_manual(values=(whatever)). Here you want scale_fill_manual.

ggplot(data=sdf,aes(x=hours,y=count,group=machine,fill=machine))+
  geom_area(position="dodge") + 
  scale_fill_manual(values=c("red", "darkorchid", "green"))

Note that, as a rule, you want to let ggplot group the data for you, as you have done in your second ggplot call (This is what the group argument does). Supplying each 'slice' of data separately, as you have done in your first example, pretty much defeats the purpose of ggplot2, and should be avoided.

来源：https://stackoverflow.com/questions/18519243/ggplot-legend-key-color-and-items