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st: RE: xlabels and graph with 2 y-axis


From   "Nick Cox" <n.j.cox@durham.ac.uk>
To   <statalist@hsphsun2.harvard.edu>
Subject   st: RE: xlabels and graph with 2 y-axis
Date   Thu, 21 Aug 2003 15:48:11 +0100

Dr Veit Grote

> I have a simple graph that does not come out as I want to 
> (Stata 8.1).
> I have a labeled categorical variable which I would like to 
> use as my x-axis, and two numerical variables of different 
> scales (2 y-axis). One should be expressed in bars and one 
> as a line/connected line (as in the frequency polygon 
> example in Statalist just recently).
> 
> 1. First problem: Why is the scale of the bars cut (in my 
> data at 30, so that the lower range 0-30 is not displayed) 
> whereas the scale of the 2nd y-axis is for the whole range 
> of the data? OK, I fixed that with options scale/range.

Not sure what kind of answer you want. It's just the way it's 
implemented. 

Evidently one design would ensure that by default all bars in 
-twoway bar- start at 0, but that would be awkward. 

Put it whimsically: the graph's primary identity is 
as a -twoway- graph, and only secondarily is it a -bar- 
graph. The rule for -twoway-'s default is _not_ to 
insist on starting axes at 0. That's what takes precedence 
here. At least, that's my interpretation. 

Admittedly, the rule causes puzzles at times. I have been 
caught a few times wondering why some of my bars had 
disappeared and searched for my bug as an explanation. 
This happened when I was developing -eqprhistogram-, which 
is really a wrapper for -twoway bar-. After having worked out 
what was going on, with an excellent assist
from Vince Wiggins, I wired in -yscale(range(0))- as 
a default. 

> 2. Second problem: I am unable to display the labels of the 
> x-axis? What is the trick? One desperate try was:
> 
> twoway bar y1 x || connected y2 x, xlabel(#7, valuelabels) yaxis(2)

I got the value labels to appear when I insisted -legend(off)-. 
Can't explain that one at all.  

Nick 
n.j.cox@durham.ac.uk 

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