[R] making scatter plot points fill semi-transparent
Steve Lianoglou
mailinglist.honeypot at gmail.com
Thu Aug 6 06:09:10 CEST 2009
Hi,
On Aug 5, 2009, at 11:48 PM, per freem wrote:
> hi all,
>
> i have a simple scatter plot, and i'd like to make it so the scatter
> plot colors are slightly transparent. i see in a previous post that
> someone mentioned the "alpha" parameter, but i am not sure how it can
> be used with the 'plot' function [*].
>
> for example, suppose i have:
>
> plot(mydata$column1, mydata$column2, col="red", cex=1)
>
> i now want to make it so the color of these points (in this case red)
> is slightly transparent, which will make overlap between them very
> obvious. i realize that hexbin and other density plot methods are used
> to make this, but i am using it for a different purpose, and so i just
> want the points to be transparent without any binning or shading.
>
> a previous poster suggested:
>
> plot( rnorm(1000), rnorm(1000), col="#0000ff22", pch=16,cex=3)
>
> but i don't understand this color notation.
It's the usual #RRGGBB color notation, w/ the last two digits
apparently defining the amount of opacity.
#0000FFFF is blue w/ full opacity
To figure out how to define your color with RGB notation, use a mix of
col2rgb and rgb functions:
R> col2rgb('blue', alpha=T)
[,1]
red 0
green 0
blue 255
alpha 255
R> rgb(red=0, green=0, blue=255, alpha=255, max=255)
[1] "#0000FFFF"
Play with different values of alpha (0 < alpha <= 255) in the above
call to get different levels of opacity for your points.
R> rgb(red=0, green=0, blue=255, alpha=10, max=255)
[1] "#0000FF0A"
R> plot( rnorm(1000), rnorm(1000), col="#0000FF0A", pch=16,cex=3)
> is there any way to pass
> in the usual col="colorname" argument and then tweak that color's
> transparency?
Maybe, but I'm not familiar with it.
-steve
--
Steve Lianoglou
Graduate Student: Computational Systems Biology
| Memorial Sloan-Kettering Cancer Center
| Weill Medical College of Cornell University
Contact Info: http://cbio.mskcc.org/~lianos/contact
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