R help - Sep 2007 - Histogram with colors

Is there a simple way to plot a histogram with colors?

For example, suppose I generate random points in the
N(2,1) distribution:

  x <- rnorm(100000, mean = 2, sd = 1)

Now I would like to plot the histogram:

  hist(x)

but I would like to show the bars with x < 0 in red, and the
bars with x >= 0 in lightgreen. Is there any simple way to
do it?

I think I can do it in two steps:

  x.hist <- hist(x, plot=FALSE)
  plot(x.hist, col=c(rep("red", 5), rep("green", 12)))

but maybe a more direct way is available.

Alberto Monteiro

Not really but a better plot call would be


plot(x.hist,col=ifelse(x.hist$breaks<0,"red","green"))

Ross Darnell


-----Original Message-----
From: r-help-bounces at r-project.org [mailto:r-help-bounces at r-project.org]
On Behalf Of Alberto Monteiro
Sent: Tuesday, 18 September 2007 6:12 AM
To: r-help at stat.math.ethz.ch
Subject: [R] Histogram with colors

Is there a simple way to plot a histogram with colors?

For example, suppose I generate random points in the
N(2,1) distribution:

  x <- rnorm(100000, mean = 2, sd = 1)

Now I would like to plot the histogram:

  hist(x)

but I would like to show the bars with x < 0 in red, and the
bars with x >= 0 in lightgreen. Is there any simple way to
do it?

I think I can do it in two steps:

  x.hist <- hist(x, plot=FALSE)
  plot(x.hist, col=c(rep("red", 5), rep("green", 12)))

but maybe a more direct way is available.

Alberto Monteiro

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On 9/17/07, Alberto Monteiro <albmont at centroin.com.br>
wrote:
> Is there a simple way to plot a histogram with colors?
>
> For example, suppose I generate random points in the
> N(2,1) distribution:
>
>   x <- rnorm(100000, mean = 2, sd = 1)
>
> Now I would like to plot the histogram:
>
>   hist(x)
>
> but I would like to show the bars with x < 0 in red, and the
> bars with x >= 0 in lightgreen. Is there any simple way to
> do it?
You can do this with ggplot:

install.packages("ggplot2")
library(ggplot2)
qplot(x, geom="histogram", data=data.frame(x), fill = factor(x >=
0))

You can find out more at http://had.co.nz/ggplot2.

Hadley

>>> "Alberto Monteiro" <albmont at centroin.com.br>
17/09/2007 21:11:51 >>>
>Is there a simple way to plot a histogram with colors?
>
>I think I can do it in two steps:
>
>  x.hist <- hist(x, plot=FALSE)
>  plot(x.hist, col=c(rep("red", 5), rep("green", 12)))
>
>but maybe a more direct way is available.
Not really, unless you specify breaks= in the histogram call. You will need to
know the number of bins to specify the colours correctly, so you need a
histogram object.

But you can use the histogram object itself to choose which bars to colour:
 x<-rnorm(150)
x.hist<-hist(x, plot=F)
plot(x.hist, col=ifelse(x.hist$mids>0,"green","red"))

$mids holds the midpoints of the bins, so it will always give you a vector of
the right length for the colours.

You can compress this into one line:
plot(x.hist<-hist(x, plot=F),
col=ifelse(x.hist$mids>0,"green","red"))

but it's really the same number of operations, so it gains little.


Steve ellison


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