# [R] Adding percentage to Pie Charts (was (no subject))

Anupam Tyagi AnupTyagi at yahoo.com
Tue Sep 19 08:51:51 CEST 2006

```Greg Snow <Greg.Snow <at> intermountainmail.org> writes:

>
> You may want to rethink your whole approach here:
>
> 1. Pie charts are usually a poor choice of graph, there are better
> choices.
> 2. Adding percentages to a pie chart is a way of admitting that the pie
> chart is not doing the job.
> 3. If you want people to compare percentages, then a table is what is
> needed.
> 4. A pie chart with percentages added is essentially a colorful but
> poorly layed out table.
>
> Consider using a dotplot instead of a pie chart, it changes the job of
> the viewer from comparing areas/angles (done poorly by humans) to
> comparing positions along a common scale (done well by humans).

I think dot charts (plots) are very useful, but they are not substitutes for a
pie chart: they do not show a comparison between the total and the individual
value; have a different scale (linear, usually), and are visually not suitable
to answer some questions that a pie chart can answer (is the value approximately
less than a fourth of the total? Is it less than half?). For some of these
questions, even dot-charts require a value label, or the user doing mental
calculations to guess approximations.

I think I am quite attuned to getting approximate fractions from a pie-chart in
shorter time, than on a linear scale like the dot-chart.

A modification in a pie chart that draws overlapping areas with a common start
point at the top of the circle, can make is more informative than a dot-chart.
Something like:
* Start drawing at the top of the circle, as zero (degree/area).
* Draw the representation of every value starting from the top, as zero,
representing it as a labled line from the center of the circle to the boundary
(can use colors where possible).
* Use two lables for the circular axis, inside one for percentages, outside for
values.

What is the simplest way to draw this in R?

Anupam.

```