[R] specify breaks in divergent palette in RColorBrewer: was divergent colors around zero in levelplot()

Don McKenzie dmck at u.washington.edu
Tue Nov 26 18:48:13 CET 2013


Thanks to everyone who weighed in on this.  I found a naive solution that was good enough for my needs, and it may take me a bit to get the subtleties
of your comments.

On Nov 26, 2013, at 2:12 AM, Barry Rowlingson <b.rowlingson at lancaster.ac.uk> wrote:

> On Tue, Nov 26, 2013 at 9:58 AM, Prof Brian Ripley
> <ripley at stats.ox.ac.uk> wrote:
> 
>>>  But the image function (and probably levelplot) doesn't allow that so
>> 
>> Mis-information alert!   The help says
>> 
>>      col: a list of colors such as that generated by ‘rainbow’,
>>           ‘heat.colors’, ‘topo.colors’, ‘terrain.colors’ or similar
>>           functions.
>> 
>> and look at what they generate.  Or see e.g. ?col2rgb .
>> 
>> Although base graphics has the concept of a palette of colours, AFAIK it
>> has always been bolted on top of a general colour specification,
>> originally RGB and for many years already RGBA.
> 
> 
> Yes image allows you to specify col=, but it always specifies a
> palette. The matrix values are scaled from 1:length(col) and looked up
> in that palette. You can't call image with z as matrix of colours and
> get those colours, nor set col to a matrix of colours and a see those
> colours laid out. This is unlike points() where specifying col= as a
> vector of the same length as the number of points gives you a 1:1
> mapping of points to colours.
> 
> To do image() with a 1:1 mapping of cell values to colours requires a
> tiny bit of hoop-jumping.
> 
> Barry
> 
> ______________________________________________
> R-help at r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.

Don McKenzie
Research Ecologist
Pacific Wildland Fire Science Lab
US Forest Service

Affiliate Professor
School of Environmental and Forest Sciences
University of Washington
dmck at uw.edu



More information about the R-help mailing list