[R] barplot2, gap.barplot

[hadley wickham]

On 3/2/07, Marc Schwartz <marc_schwartz at comcast.net> wrote:
> On Fri, 2007-03-02 at 08:53 -0600, hadley wickham wrote:
> > > 3. Depending on the nature of your data, if the extreme value is
> > > representative of an important marked difference relative to the other
> > > values, then I don't particularly find the 'look' of the plot to be
> > > overly problematic. It does appropriately emphasize the large
> > > difference.
> > >
> > > On the other hand, you might want to consider using a log scale on the y
> > > axis as an alternative to an axis gap. This would be a reasonable
> > > approach to plotting values that have a notable difference in range.  If
> > > you do this, note that you would need to ensure that all y values are >0
> > > (ie. y axis range minimum, lower bounds of CI's, etc.) since:
> > >
> > > > log10(0)
> > > [1] -Inf
> > >
> > >
> >
> > Of course, you can't do this with a bar plot, because bars should be
> > anchored at 0.
>
> Both barplot() and barplot2() support log scaling for both x and y axes.
>
> In both functions, the default axis minimum for the 'height' axis (y by
> default, x if 'horizontal = TRUE') will be 0.9 * min(height) to avert
> log10(0) related issues. Errors will be issued otherwise if any values
> of 'height' are <= 0 or 'ylim'/'xlim' args are similarly set.

I think that's a pretty bad idea - in a bar plot you are comparing the
ratio of heights of the bars, not the absolute heights.  It's the same
reason it's a bad idea to have a bar graph with a non-0 y-axis - it's
misleading.

Hadley