Histogram with a non zero origin

[Pierre B. de Villemereuil]

Dear all,

I'm trying to plot a histogram of values around 95%. For easier reading,
I'd like to start histogram at 60% instead of zero. Unfortunately, I
couldn't find a way to do it !

Here is a reproducible example:
y<-runif(16,0.6,1)
x<-c(rep("A",4),rep("B",4),rep("C",4),rep("D",4))
type<-rep(c("1","2","3","4"),4)
data<-data.frame(x=x,y=y,type=type)

Here is a plot starting from zero :
ggplot(data,aes(x=x,y=y))+geom_bar(aes(fill=type),colour='black',position="dodge",stat="identity")+scale_y_continuous(formatter="percent")

However, when "limiting" y values, the plot just disappears:
ggplot(data,aes(x=x,y=y))+geom_bar(aes(fill=type),colour='black',position="dodge",stat="identity")+scale_y_continuous(limits=c(0.6,1),formatter="percent")

I also tried to use the (not documented) "origin" argument of stat_bin()
function, but it is exactly identical to the first plot (seems like
"origin" does nothing):
ggplot(data,aes(x=x,y=y))+stat_bin(aes(fill=type),colour='black',position="dodge",origin=0.6,geom="histogram")+scale_y_continuous(formatter="percent")

Does anyone has an idea how to start a histogram from an arbitrary value
instead of 0 ?

Thanks in advance for any help !

Cheers,
Pierre.

[Winston Chang]

Pierre -

You can use coord_cartesian to set the viewing area of the graph. When you use scale_y_continuous, it also clips the data to fit into the range -- any bars that extend out of the range will not show.

This should do the trick:

ggplot(data,aes(x=x,y=y)) +

    geom_bar(aes(fill=type),colour='black',position="dodge",stat="identity") +

    coord_cartesian(ylim=c(.6,1))

Using coord_cartesian doesn't change the placement of the ticks, however, so you may need to specify the breaks in scale_y_continuous manually, with something like this:

ggplot(data,aes(x=x,y=y)) +

    geom_bar(aes(fill=type),colour='black',position="dodge",stat="identity") +

    coord_cartesian(ylim=c(.6,1)) +

    scale_y_continuous(breaks=seq(0,1,.1))

In the development version of ggplot, there's no need to use coord_cartesian; you can have bars go out of the viewable range by setting scale_y_continuous.


Also, "origin" sets the starting point along the x axis (not y) for geom_histogram.

Hope this helps,
-Winston

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[Hadley Wickham]

> In the development version of ggplot, there's no need to use
> coord_cartesian; you can have bars go out of the viewable range by setting
> scale_y_continuous.

That might be a bug...

Hadley

--
Assistant Professor / Dobelman Family Junior Chair
Department of Statistics / Rice University
http://had.co.nz/

[Winston Chang]

Really? I've actually found it very useful to have things work this way...

[Hadley Wickham]

Yes, I'm not sure yet if I want to change the behaviour or not. It
certainly needs to be done with some thought (especially the
implications for setting limits on legends)

Hadley