[R] levelplot question

[Greg Snow]

From the help for panel.levelplot in the section on 'col.regions':

" the exact number being one
          more than the length of 'at'"

was what I based my assumption on (also the "not longer than at" phrase in the last sentence on recycling).

The second part was somewhat speculation on my part, automatically adding -Inf and Inf would mean that you would not need to make sure to span the range of the data, but on the other hand, it would make it hard to exclude values outside the region as in your example, arguments could be made for either direction, the current behavior is probably best overall.

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


> -----Original Message-----
> From: Deepayan Sarkar [mailto:deepayan.sarkar at gmail.com]
> Sent: Wednesday, May 06, 2009 6:35 PM
> To: Greg Snow
> Cc: Antje; r-help at stat.math.ethz.ch
> Subject: Re: [R] levelplot question
> 
> On Tue, May 5, 2009 at 8:58 AM, Greg Snow <Greg.Snow at imail.org> wrote:
> > The function that is doing the color assignments is level.colors in
> the lattice package.
> > Looking at the code confirms that the number of colors should be 1
> less than the length
> > of the at variable (the documentation implies that it should be 1
> more, looks like a documentation bug to me).
> 
> Could you point to the place where this is implied? I couldn't see
> anything obviously wrong in ?levelplot or ?level.colors.
> 
> > It is possible that at one time the author intended to prepend -Inf
> and append Inf to the at
> > vector so that it did not need to span the entire range of the data,
> but that was not implemented.
> > I think I would prefer that fix to changing the documentation.
> 
> That is a slightly different issue though: e.g.,
> 
> > level.colors(c(1, 2, 3), at = c(1.5, 2.5, 3.5), colors = FALSE)
> [1] NA  1  2
> 
> The first value doesn't fall in any interval, so gets a NA.
> 
> level.colors() is mainly a helper function for levelplot(), and it is
> important there that the first and last intervals not be open-ended.
> levelplot() has no 'zlim' argument, and you need 'at' to restrict the
> values shown, e.g.,
> 
> levelplot(volcano, at = do.breaks(c(120, 200), 10))
> 
> -Deepayan