[R] Automatic anchors for text boxes

Yves Moisan
2007-08-31T13:20:38Z

Hi All,

I'm struggling to add text automatically to plots.  I have a series of
scatterplots that I have stored in a script because the underlying data
changes often and the plots need to be regenerated.  I use the scatterplot
function (defined in Rcmd, I believe).  When one of the variables is a
factor, a boxplot is drawn over the scatter of the other variable.  In the
case where x is a factor with 10 values, I'll see 10 vertical boxplots.  So
far, so good.

I was asked to show other stats on top of those scatterplots, e.g. mean,
number of observations, etc.  I can find those values, but the problem is I
don't know how to put them on the plot, given I don't want to look at
each
plot one by one and manually identify the locations where I need to add the
text.  I was wondering if something like a pseudo label (I want to keep the
original axis labels) existed that could be used to anchor a text box ?  Or
maybe a semi-manual approach where I could offset such a pseudo-label
position along the y axis?  Since I know the size of my resulting jpegs, I
could use a constant y offset for the text and they'd be aligned properly
along the x axis because they are labels.   For the mean value, I could draw
a short horizontal line segment across the boxplot, but again I'd have the
problem of tying that line segment to specific x-axis values so they
intersect the right boxplot.  Any clues ?

On a related note, I've added regression lines, again by factor (thanks
scatterplot!), and was asked to write the regression equation in plain text.
I have between one and 7 lines on the plots, so again how could I
automatically tie a text box, this time to a specific regression line ?
Maybe that would be easier using a legend, but it would be nice to be able
to write the equation alongside the line.

TIA
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