[R] Use of colour in plots

Steve Murray smurray444 at hotmail.com
Thu Sep 18 21:02:19 CEST 2008


Thanks for this - it works really well! 

One (hopefully final!) question I have is, is there any way of preventing overplotting? I'm finding that many of the red points are being obscured by the greens - I've tried making the point sizes small (cex=0.1) but this doesn't fully solve the problem.

Or even, is there a way of changing the order of which the points are plotted?

Thanks again,


> From: Greg.Snow at imail.org
> To: smurray444 at hotmail.com; thierry.onkelinx at inbo.be; petr.pikal at precheza.cz; jrkrideau at yahoo.ca; jim at bitwrit.com.au
> CC: r-help at r-project.org
> Date: Thu, 18 Sep 2008 10:56:05 -0600
> Subject: RE: [R] Use of colour in plots
> Try something like:
>> x <- runif(25)
>> y <- rnorm(25)
>> z <- rnorm(25, 3*x)
>> plot(x, y, col=ifelse( z> 1.25, 'red', 'green') )
> Does this help,
> --
> 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 Steve Murray
>> Sent: Thursday, September 18, 2008 8:14 AM
>> To: ONKELINX, Thierry; Petr PIKAL; jrkrideau at yahoo.ca;
>> jim at bitwrit.com.au
>> Cc: r-help at r-project.org
>> Subject: Re: [R] Use of colour in plots
>> Jim and all,
>> Maybe I've misunderstood ?color.scale (appologies if this is so), but I
>> don't think this is what I need. I'm not looking to scale the colours
>> of points, instead I simply want to assign each point a colour (either
>> red or green) based on it's value in the Urban.Rural column.
>> To clarify (but please also see my earlier message if this helps):
>> In my dataset (Jan) I have 3 columns of interest: Average Burnt Area
>> Fraction (ABAF), PopDensity and Urban.Rural.
>> I want to plot ABAF against PopDens (which I've had no problems doing)
>> and then, regardless of the values of ABAF and PopDens, I want to
>> assign it a colour. The colour each point is given is based on the
>> corresponding Urban.Rural value on each row. If for each pair of ABAF
>> and PopDens values the Urban.Rural value on that row is>1.25, then the
>> point should be coloured red, whereas if it's =
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