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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