R- split histogram according to factor level

Question

This is my data:

type<-rep(c(0,1),100) 
diff<-rnorm(100)
data<-data.frame(type,diff)

If I want to plot historgram of diff , I do this:

hist(data$diff)

But what I want to do to split my histogram according to type . I could do this:

par(mfrow=c(1,2))
hist(data$diff[data$type==0])
hist(data$diff[data$type==1])

But what this is giving me are two different histograms side by side. What I want to do is produce a single histogram with diff of 0 at one side and diff of 1 at other side. Something like this with bars as continuous without the breaks or border in between. This presumably would mean the axis will be split into two for each factor.

Answer 1

You can use the ggplot2 package:

library(ggplot2)

ggplot(data,aes(x=diff))+geom_histogram()+facet_grid(~type)+theme_bw()

You can also put them on the same plot by "dodging" them:

ggplot(data,aes(x=diff,group=type,fill=type))+
  geom_histogram(position="dodge",binwidth=0.25)+theme_bw()

If you want them to overlap, the position has to be position="identity"

ggplot(data,aes(x=diff,group=type,fill=type))+
  geom_histogram(position="identity",alpha=0.5,binwidth=0.25)+theme_bw()

If you want them to look like it does in the first one but without the border, you have to hack it a little:

data$diff[data$type==1] <- data$diff[data$type==1] + 6

ggplot(data,aes(x=diff,group=type,fill=type))+
  geom_histogram(position="identity",alpha=0.5,binwidth=0.25)+theme_bw()+
  scale_x_continuous(breaks=c(-2:2,4:8),labels=c(-2:2,-2:2))

Answer 2

That plot was made using the lattice package

set.seed(1)
type<-rep(c(0,1),100) 
diff<-rnorm(100)
data<-data.frame(type,diff)


library('lattice')
histogram(~ diff | type, data = data)

here is how you can do it in base graphics

## first plot - left half of x-axis, right margin set to 0 lines
par(fig = c(0, .5, 0, 1), mar = c(5,4,3,0))
hist(data$diff[data$type==0], ann = FALSE, las = 1)

## second plot - right half of x-axis, left margin set to 0 lines
par(fig = c(.5, 1, 0, 1), mar = c(5,0,3,2), new = TRUE)
hist(data$diff[data$type==1], ann = FALSE, axes = FALSE)
axis(1)
axis(2, lwd.ticks = 0, labels = FALSE)

title(main = 'Histogram', xlab = 'x label', outer = TRUE, line = -2)