[R] Specifying relative position of text in a plot

[Nordlund, Dan (DSHS/RDA)]

> -----Original Message-----
> From: r-help-bounces at r-project.org 
> [mailto:r-help-bounces at r-project.org] On Behalf Of Alberto Monteiro
> Sent: Wednesday, March 12, 2008 10:28 AM
> To: Tom La Bone; r-help at r-project.org
> Subject: Re: [R] Specifying relative position of text in a plot
> 
> 
> Tom La Bone asked:
> >
> > What is the simplest way to specify the location of text in a 
> > scatter plot
> > (created using the plot function) in relative terms rather than 
> > specific x-y coordinates? For example, rather than putting text at 
> > (300,49) on a plot, how do I put it 1/10 of the way over from the y 
> > axis and 1/2 of the way up from the x axis? Thanks.
> > 
> See the help of par:
> ?par
> 
> Namely:
> 
> plot(rnorm(100), rnorm(100))
> pu <- par()$usr
> x <- pu[1] * 0.5 + pu[2] * 0.5
> y <- pu[3] * 0.1 + pu[4] * 0.9
> text(x, y, "the quick brown fox jumps over a lazy dog")
> 
> Alberto Monteiro
> 

This is a useful example of placing text, but I interpreted the request as aking for the text to be placed at the left side of the graph (1/10 of the x range) and centered vertically (with respect to the y scale).  So, then I would calculate x and y as

x <- pu[1] * 0.9 + pu[2] * 0.1
y <- pu[3] * 0.5 + pu[4] * 0.5

Also, text() centers the supplied text at the x,y coordinates. So, if Tom wants the text "begin" at that point, he will need to adjust the x coordinate for the length of the string being printed.

Hope this is helpful,

Dan

Daniel J. Nordlund
Research and Data Analysis
Washington State Department of Social and Health Services
Olympia, WA  98504-5204