On May 14, 2010, at 9:59 AM, Justin Fincher wrote:
> I have two datasets that I would like to plot in a single figure. The first
> plot is generated by a function that then takes a subset of the data. (It
> is biological data so it is usually by chromosome e.g.
> function(data1,subset="chr8") ) Since not only are the chromosomes different
> sizes, but across different datasets there may be different numbers of
> points for a single chromosome, I do not know the coordinates on the x-axis
> prior to running the function.
>
> I want the scale of the second plot to align to that of the first, but I
> don't know how to find the default xlim for the graph generated by the
> function. Is there any way to access this information so I can then pass it
> to the plot() of the second plot? Thanks!
>
> - Fincher
The result of par("usr") will give you the actual limits of the x and y axes
(plot region) once the first graphic is drawn to the device. See ?par for more
information. Note that by default, R will extend the data ranges by 4% (see
'xaxs' in ?par).
However, you are better off getting the common ?range of the relevant values in
both subsets of data before plotting and then explicitly set the same x and y
axis ranges in each plot by using the 'xlim' and 'ylim' arguments to plot().
HTH,
Marc Schwartz
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