MaplePrimes - answers and comments on Question, How doi I insert a legend in a PieChart from the command lines?

How about this:

epostma — Fri, 16 Jul 2010 00:28:59 Z

PieChart and the like should really have a legend option, and maybe I will at some point get around to that. Until then, here is a command that will match the sectors up with the left hand sides of your list T:

Q := subs(zip((pol, legend) -> pol = op(0, pol)(op(pol), LEGEND(legend)), select(type, [op(P)], specfunc(anything, POLYGONS)), map(lhs, T)), P):
plots[display](Q, title = ["Distribución de las exportaciones de Chile en el año 2009", font = [TIMES, BOLD, 18]], font = [TIMES, BOLD, 12]);

This is not necessarily guaranteed to work in all cases, I'm afraid. Making a legend for the PieChart plot structure after the plot has been generated cannot really be done reliably. But still, it will work in a large number of cases in versions of Maple that are currently available - and it works for this particular plot in Maple 12.

Hope this helps,

Erik Postma
Maplesoft.

Another workaround

pchin — Fri, 16 Jul 2010 01:12:42 Z

Here's another possibility:

Create a bunch of empty polygons having the same colours as those you've defined for the pie chart and include these in your plot.

> colorlist := ["red", "Orange", ...];
> legendlist := ["first entry", "second entry", ...];
> p1 := plots[display](seq(plots[polygonplot]([[0,0],[0,0]], color=colorlist[i], legend=legendlist[i]), i=1..nops(colorlist))):
> plots[display](p1, p2);

where p2 is the pie chart plot.

Paulina

Thank you very much, but I have a problem.

pepa — Fri, 16 Jul 2010 01:55:14 Z

Thank you very much, but I have a problem. I inserted the line:

Q := subs(zip((pol, legend) -> pol = op(0, pol)(op(pol), LEGEND(legend)), select(type, [op(P)])))

before of the "plots[display](Q,......), etc..

and showed: "Error, incorrect number of extra arguments in select"

I don't understand very much that line. Reading the Maple Help I could understand a little more, but it doesn't work...

Can you still help?

Thanks...

MJ

Explanation

epostma — Fri, 16 Jul 2010 22:12:39 Z

@pepa : I'd recommend going with pchin's solution, which is more reliable.

Just for people reading my comment above and wondering what's going on, a quick explanation. I'll repeat that this is not necessarily a reliable way to interact with plots; the data structure may change in future versions. That said, it may offer something useful to someone wanting to operate on other Maple data structures; the same basic functions are useful elsewhere, of course.

The easiest way to deal with these sorts of things is reading it starting from the inside. The innermost thing that makes sense by itself is

select(type, [op(P)], specfunc(anything, POLYGONS));

which returns the ordered list of all POLYGONS plot structures in P (see ?type and ?type/structure and ?select). Another subexpression on the same level is

map(lhs, T);

which returns all the left hand sides for the equations in T (see ?map and ?lhs). There should be equally many of each. We apply ?zip to those two lists, and the function with which we zip them is custom: it's

(pol, legend) -> pol = op(0, pol)(op(pol), LEGEND(legend));

which takes a POLYGONS plot structure and a legend argument (one from the first list constructed above, one from the second list) and creates from it an equation, where the left hand side is pol (the POLYGONS plot structure) and the right hand side is the same plot structure but with an extra argument: LEGEND(legend).

The resulting list of equations is fed to ?subs, so that it substitutes the version with the extra argument for the original version of each POLYGONS data structure, and that's it.

I'll finish by repeating my recommendation that you use pchin's idea of adding a couple empty polygons with a legend, for the question you originally asked.

HTH,

Erik Postma
Maplesoft.