Re: [R] Labelling curves on graphs

From: Frank E Harrell Jr <f.harrell_at_vanderbilt.edu>
Date: Thu, 17 Jul 2008 06:30:34 -0500

Barry Rowlingson wrote:
>
> Why use color when you can use black and label the curves where they
> are most separated? This solves problems with color blindness,
> xeroxing, and faxing.
>
> Where should I put the labels in this example:
>
> > set.seed(123)
> > z=matrix(runif(6*50),50,6)
> > matplot(z,type='l',col=1,lty=1)
>
> A label is only going to indicate which curve is which at a point. If
> the curves approach or cross anywhere you're going to get confused. Line
> styles and colours persist along the length of the line.
>
> For nice smooth well-behaved curves then perhaps labelling is okay -
> contour lines rarely cross, and even when they do they must have the
> same height value anyway.
>
> I'm not sure once you get to six lines on a graph you can find six
> distinctive line styles without using colour, so it might be better to
> switch graphic completely. Compare the above plot with image(z).
>
> If the plots don't cross, one solution is to extend the plot to the
> right and just add labels there:
>
> > set.seed(123)
> > z=matrix(runif(6*50),50,6)
> > m=apply(z,1,cumsum)
> > ms=apply(m,1,sort)
> > matplot(ms,type='l',xlim=c(0,55),lty=1,col=1)
> > text(50,ms[50,],c("Foo","Bar","Baz","Qux","Quux","Quuux"),adj=-0.1)
>
> I can't see a neater way of putting labels actually on the lines in this
> case - they'll be all over the place to squeeze them in the gaps.
>
> Barry
>

Barry - you're right; when two lines cross more than 2 or 3 times the suggested approach doesn't work well. When it does work, not having the user have to look at a legend is a benefit.

Depending on the number of lines, using thick gray scale and thin black lines can be very effective.

Frank

-- 
Frank E Harrell Jr   Professor and Chair           School of Medicine
                      Department of Biostatistics   Vanderbilt University

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Received on Thu 17 Jul 2008 - 11:34:53 GMT

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