R help - Aug 2007 - Selectively shading areas under two density curves

Dear Listers,

I am drawing a plot of two density curves, for male and female incomes. I would 
like to shade/hatch/color (whatever) the areas under the curves which are 
distinctive for each gender. This is the code I have tried so far:


m <- density(topmal.d$y, bw = "sj")
f <- density(topfem.d$y, bw = "sj")
par(mfrow = c(1,1))
plot(x = c(0,400), y = c(0,0.02), type = "n",
     bty = "l", xlab = "Annual earnings (in $thousands)",
ylab = "Density")
polygon(m, col = "blue", border = "blue", density = 20,
angle = -45)
polygon(f, col = "red", border = "red", density = 20, angle
= 45)


Without the data I realise you may not be able to see my goal. But basically the
  m density and the f density overlap for most of the plot, but areas
"bulge"
out on the left and right of the overlapped area. What I'm wanting to do is 
shade/hatch/color etc these areas which are unique to each density, that is, 
which are outside the overlapped area.

My code is successful at hatching the bulging areas, but leaves me with a double
hatched area for the overlap, which is distracting. If I could turn this double 
hatched area white, that would achieve my goal, though ideally I would like to 
be able to specify something like "shade only areas under the m density
curve
which are not also under the f density curve (and shade only under the f density
curve those areas not under the m density curve".

Any advice would be most appreciated.

I am using R 2.5.1. under Windows XP.

Kind regards
Ian Watson

Ian Watson wrote:
> Dear Listers,
> 
> I am drawing a plot of two density curves, for male and female incomes. I
would
> like to shade/hatch/color (whatever) the areas under the curves which are 
> distinctive for each gender. This is the code I have tried so far:
> 
> 
> m <- density(topmal.d$y, bw = "sj")
> f <- density(topfem.d$y, bw = "sj")
> par(mfrow = c(1,1))
> plot(x = c(0,400), y = c(0,0.02), type = "n",
>      bty = "l", xlab = "Annual earnings (in
$thousands)", ylab = "Density")
> polygon(m, col = "blue", border = "blue", density = 20,
angle = -45)
> polygon(f, col = "red", border = "red", density = 20,
angle = 45)
> 
> 
> Without the data I realise you may not be able to see my goal. But
basically the
>   m density and the f density overlap for most of the plot, but areas
"bulge"
> out on the left and right of the overlapped area. What I'm wanting to
do is
> shade/hatch/color etc these areas which are unique to each density, that
is,
> which are outside the overlapped area.
> 
> My code is successful at hatching the bulging areas, but leaves me with a
double
> hatched area for the overlap, which is distracting. If I could turn this
double
> hatched area white, that would achieve my goal, though ideally I would like
to
> be able to specify something like "shade only areas under the m
density curve
> which are not also under the f density curve (and shade only under the f
density
> curve those areas not under the m density curve".
> 
Hi Ian,
Once you get used to the vagaries of "density" output, this isn't
too
hard, as you only have one crossing. I think this gets you what you want:

minc<-rnorm(1000,mean=65000,sd=15000)
finc<-rnorm(1000,mean=55000,sd=15000)
m <- density(minc, bw = "sj")
f <- density(finc, bw = "sj")
plot(m$x,m$y,main="Male vs female income distribution",
 
xlab="",ylab="Density",type="l",xaxt="n")
library(plotrix)
axis.mult(1,at=c(0,20000,40000,60000,80000,100000,120000),mult=1000,
 
labels=c("0","20","40","60","80","100","120"),mult.label="Annual
income/1000")
lines(f$x,f$y)
fontop.end<-max(which(f$y>m$y))
xend<-length(f$x)
polygon(c(f$x[1:fontop.end],rev(m$x[1:fontop.end])),
  c(f$y[1:fontop.end],rev(m$y[1:fontop.end])),col="red")
fontop.end<-fontop.end+1
polygon(c(f$x[fontop.end:xend],rev(m$x[fontop.end:xend])),
  c(f$y[fontop.end:xend],rev(m$y[fontop.end:xend])),col="blue")

Jim