R help - Jul 2010 - Constrain density to 0 at 0?

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?



Thanks



Robert Farley
Metro
1 Gateway Plaza
Mail Stop 99-23-7
Los Angeles, CA 90012-2952
Voice: (213)922-2532
Fax:    (213)922-2868
www.Metro.net



	[[alternative HTML version deleted]]

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.

Look at the logspline package.  This is a different approach to density
estimation from the kernel densities used by 'density', but does allow
you to set fixed boundaries.

-- 
Gregory (Greg) L. Snow Ph.D.
Statistical Data Center
Intermountain Healthcare
greg.snow at imail.org
801.408.8111

> -----Original Message-----
> From: r-help-bounces at r-project.org [mailto:r-help-bounces at r-
> project.org] On Behalf Of Farley, Robert
> Sent: Monday, July 19, 2010 7:57 PM
> To: r-help at r-project.org
> Subject: [R] Constrain density to 0 at 0?
> 
> 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?
> 
> 
> 
> Thanks
> 
> 
> 
> Robert Farley
> Metro
> 1 Gateway Plaza
> Mail Stop 99-23-7
> Los Angeles, CA 90012-2952
> Voice: (213)922-2532
> Fax:    (213)922-2868
> www.Metro.net
> 
> 
> 
> 	[[alternative HTML version deleted]]
> 
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