On Jul 20, 2010, at 2:45 PM, Farley, Robert wrote:
"Read the help page for density more carefully. Especially the bw and
from arguments."
Yes, it was my inability to make sense of the help page that
motivated my email.
My distances range from 0.4 to 7.6 but the density plot ranges from
-2 to 10.
"from=0" seems to hide the negative portion of the density without
setting it to 0.
I've tried adjust, but it requires a value of 0.2, which results in
a very, very spiky plot.
I was hoping for a process that could "forbid" impossible (negative)
values, yet allow the density plot to blend the individual
measurements. Is there a "variable bw" that could be set small at
the extrema, and larger in the range of the data?
The best answer may depend on what your (unstated) goals are. Have you
considered fitting a log-Normal or Gamma distribution to the data? You
could plot the histogram and then overlay a smooth fitted distribution
curve.
?hist
require(MASS)
?fitdistr
--
David.
-----Original Message-----
From: David Winsemius [mailto:dwinsem...@comcast.net]
Sent: Monday, July 19, 2010 19:31
To: Farley, Robert
Cc: r-help@r-project.org
Subject: Re: [R] Constrain density to 0 at 0?
On Jul 19, 2010, at 9:57 PM, Farley, Robert wrote:
I'm plotting some trip length frequencies using the following code:
plot( density(zTestData$Distance, weights=zTestData$Actual),
xlim=c(0,10),
main="Test TLFD",
xlab="Distance",
col=6 )
lines(density(zTestData$Distance, weights=zTestData$FlatWeight),
col=2)
lines(density(zTestData$Distance, weights=zTestData$BrdWeight ),
col=3)
which works fine except the distances are all positive, but the
densities don't drop to 0 until around -2 or -3.
Is there a way for me to "force" the density plot to 0 at 0?
Yes. (Assuming it can be zero, given the data.)
Read the help page for density more carefully. Especially the bw and
from arguments.
--
David.
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David Winsemius, MD
West Hartford, CT
______________________________________________
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