[R] How to shade part of a density plot

[Stuart Luppescu]

I'm trying to shade part of a density plot. The code I'm trying (using
the Old Faithful data as an example) is something like this:

# The Old Faithful geyser data
data(faithful)
d <- density(faithful$eruptions, bw = "sj")
plot(d)
polygon(d[d$x>4], col = "wheat")

I expected that the part of the curve to the right of 4 on the x axis
should be shaded, but nothing gets shaded at all. In fact, when I just
try to print d[d$x>4] I get many lines of 
$"NA"
NULL
I must be mistaken in my understanding of density objects. Could someone
clear up my mistake? Thanks very much.
-- 
Stuart Luppescu       -=- s-luppescu at uchicago.edu
University of Chicago -=- CCSR 
$B:MJ8$HCRF`H~$NIc(B    -=- Kernel 2.4.18-xfs              
checkuary, n:  The thirteenth month of the year.  Begins New
 Year's Day and ends  when a person stops absentmindedly
 writing the old year on his checks. 
 
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