How to plot two histograms of different variables in one GGPlot, with legend and colours

user_15098735 0
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This is my first post on Stack Overflow, my first reproducible example, and I'm new to R, so please be gentle! I am trying to display two histograms on one plot. Each histogram is a different variable (column) in my dataframe. I can't figure out how to both colour in the bars and have the legend displayed. If I use scale_fill_manual the colours are ignored, but if I use scale_colour_manual the colours are just the outlines of the bars. If I map the colours to each histogram separately (and don't use scale_xxx_manual at all) the colours work great but I then don't get the legend.

Here is my code:

TwoHistos <- ggplot (cars) +
  labs(color="Variable name",x="XX",y="Count")+
  geom_histogram(aes(x=speed, color= "Speed"),  alpha = 0.2 ) + 
  geom_histogram(aes(x=dist, color= "Dist"), alpha = 0.2) + 
  scale_colour_manual(values = c("yellow","green"))
TwoHistos

Here is my result in an image (I pasted it but I don't know why it isn't showing up. I'm sorry!): Two histograms with outlines for colours

ggplot2 r
2 Answers

I think (if I understand you correctly), what you might want is to give a fill arguement within the geom_histogram() call.

(I've used the mtcars built-in R data here as you did not give any data to work with)

TwoHistos <- ggplot (mtcars) +
  labs(fill="Variable name",x="XX",y="Count")+
  geom_histogram(aes(x=hp, fill= "Speed",  color = "yellow"), alpha = 0.2 ) + 
  geom_histogram(aes(x=disp, fill= "Dist", color = "green"), alpha = 0.2) +
  scale_fill_manual(values = c("yellow","green"))+
  scale_colour_manual(values = c("yellow","green"), guide=FALSE)
TwoHistos

Edit: just to make really clear that I've changed the x in the geom_histogram() so it works with mtcars enter image description here

user_127171430

Use fill instead of color and use scale_fill_manual

TwoHistos <- ggplot (cars) +
  labs(color="Variable name",x="XX",y="Count")+
  geom_histogram(aes(x=speed, fill= "Speed"),  alpha = 0.2 ) + 
  geom_histogram(aes(x=dist, fill= "Dist"), alpha = 0.2) + 
  scale_fill_manual(values = c("yellow","green"))
TwoHistos

enter image description here

user_133216470
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