[R] how to plot two histograms overlapped in the same plane coordinate

[Andrew Miles]

I'm not sure what you are trying to do.  Do you want one histogram for  
males and one for females on the same graph? If so, the simplest way  
to put two histograms together is to simply use the add parameter:

age.males=age[which(sex=="M")]
age.females=age[which(sex=="F")]

hist(age.males, col="blue")
hist(age.females, add=T)

The only problem is that the hist() function does not do semi- 
transparency.  I am not sure if other packages do.  The code above  
will give you a blue histogram for males, and clear histogram for  
females on top of it.  You'll probably have to manually alter the axes  
of the histogram to give the histograms for males and females the same  
break points (i.e. where one bar stops and another begins).  See ?hist  
for more information about that.

Andrew Miles
Department of Sociology
Duke University

On Jul 9, 2010, at 9:29 AM, Mao Jianfeng wrote:

> Dear R-help listers,
>
> I am new. I just want to get helps on how to plot two histograms
> overlapped in the same plane coordinate. What I did is very ugly.
> Could you please help me to improve it? I want to got a plot with  
> semi-
> transparent overlapping region. And, I want to know how to specify the
> filled colors of the different histograms.
>
> I also prefer other solutions other than ggplot2.
>
> Many thanks to you.
>
>
> What I have done:
>
> library(ggplot2)
>
> age<-c(rnorm(100, 1.5, 1), rnorm(100, 5, 1))
> sex<-c(rep("F",100), rep("M", 100))
> mydata<-cbind(age, sex)
> mydata<-as.data.frame(mydata)
> head(mydata)
>
>
> qplot(age, data=mydata, geom="histogram", fill=sex, xlab="age",
> ylab="count", alpha=I(0.5))
>
>
> Best,
>
>
> Mao J-F
>
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