[R] image() function

[Greg Snow]

Use the zlim argument to image:

m <- matrix(1:18,3,6)

par(mfrow = c(2,1))
image(1:6, 1:3, t(m), col = rainbow(20), zlim=c(0,30))
image(1:6, 1:3, t(m+9), col = rainbow(20), zlim=c(0,30))

hope this helps,

-- 
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 Jorge Hernandez
> Sent: Friday, March 26, 2010 4:21 AM
> To: r-help at r-project.org
> Subject: [R] image() function
> 
> Hello.
> 
> I would like to know how to set the image() function so that it assigns
> colors
> relative to an absolute scale, as opposed to relative to the values
> present
> in a particular call to image().
> 
> For example:
> 
> m <- matrix(1:18,3,6)
> 
> par(mfrow = c(2,1))
> image(1:6, 1:3, t(m), col = rainbow(20))
> image(1:6, 1:3, t(m+9), col = rainbow(20))
> 
> Then the two images are identical.  But the right half of the first
> matrix
> 
> coincides (numerically) with the left half of the second.   (i.e.
> compare
> 'm' and 'm+9'.)
> 
> So the question is: how can image() (or some other function) assign the
> same color to every incidence of any given value across repeated calls
> to image()?
> 
> Thanks in advance.
> 
> JH
> 
> 
> 
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