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Re: st: Problems with -triplot-


From   Friedrich Huebler <fhuebler@gmail.com>
To   statalist@hsphsun2.harvard.edu
Subject   Re: st: Problems with -triplot-
Date   Fri, 6 Feb 2009 10:03:09 -0500

Nick,

Many thanks for your help. I now have the graph that I wanted.

Friedrich

On Fri, Feb 6, 2009 at 9:39 AM, Nick Cox <n.j.cox@durham.ac.uk> wrote:
> triplot p q r, c(l l) mcolor(pink blue)
>
> Nick
> n.j.cox@durham.ac.uk
>
> -----Original Message-----
> From: owner-statalist@hsphsun2.harvard.edu
> [mailto:owner-statalist@hsphsun2.harvard.edu] On Behalf Of Nick Cox
> Sent: 06 February 2009 13:12
> To: statalist@hsphsun2.harvard.edu
> Subject: RE: st: Problems with -triplot-
>
> Thanks to Friedrich for his comments.
>
> Fortunately, I see no real problems here.
>
> The key to understanding -separate()- is laid out tersely in the help:
>
> "separate() indicates that observations are to be subdivided into
> classes according to a
>        specified variable. A legend will be shown if and only if more
> than one class is so
>        defined. Each class is plotted as if it defined a single
> variable."
>
> Note that last sentence.
>
> To back up slightly, the one simple idea about -triplot- is that you
> feed it
>
> triplot p q r
>
> and it does some school student algebra (or trigonometry) to convert to
> that to a
>
> scatter y x
>
> together with extra bits and pieces that are of considerable cosmetic
> importance, but are nevertheless secondary to the logic.
>
> If you say -separate()-, -triplot- converts that (in your example) to a
>
> scatter y1 y2 x
>
> using no more than (surprise) the -separate- command. So you need to
> spell out
>
> scatter y1 y2 x, c(l l) mcolor(pink blue)
>
> or more precisely,
>
> triplot p q r x, c(l l) mcolor(pink blue)
>
> or whatever. Each class becomes a separate variable, and you apply
> standard -twoway- syntax to get the desired result.
>
> As for the -legend()-, -triplot- doesn't try to be smart about the
> legend but it does not have to be because you maintain full control of
> it. The default is indeed likely to be lousy. A better default would be
>
> legend(ring(0) pos(1) col(1))
>
> and perhaps I should wire that in. (Note the -legend()- pops up
> spontaneously only if -separate()- is issued, as indicated in the help.)
>
>
> If you are following along, you'll see that the way to get -triplot- to
> superimpose multiple sets of triangular coordinates is to -stack- or
> -reshape- to a long data structure with a grouping variable.
>
> Friedrich's questions have given me ideas for small improvements to your
> code and help.
>
> Nick
> n.j.cox@durham.ac.uk
>
> Friedrich Huebler
>
> To clarify my question, I would like to have separate lines, one line
> for each country.
>
> Friedrich
>
> On Thu, Feb 5, 2009 at 4:54 PM, Friedrich Huebler <fhuebler@gmail.com>
> wrote:
>> Nick Cox recently announced an updated version of his -triplot-
>> package, available from SSC. I encountered some problems with the
>> program.
>>
>> I am trying to generate a graph similar to Figure 15 in Cox (2004),
>> but with data from two countries. I would like to connect the data
>> points for each country but when I draw the graph with the options
>> c(l) and separate(country), only the points from the first country are
>> connected. Is it possible to connect the points from the second
>> country, too? Can the appearance of the markers for the second country
>> be changed? Options like mcolor() only affect the markers for the
>> first country.
>>
>> There is also a problem with the legend. At the default position below
>> the graph, the legend partly covers the label for the lower side of
>> the triangle.
>>
>> Friedrich
>>
>> Reference: Cox, Nicholas J. 2004. Speaking Stata: Graphing categorical
>> and compositional data. Stata Journal 4, no. 2: 190-215.
>> http://www.stata-journal.com/article.html?article=gr0004
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