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

Answer 1

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)

Answer 2

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))