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st: -textbarplot- available from SSC


From   "Nick Cox" <n.j.cox@durham.ac.uk>
To   <statalist@hsphsun2.harvard.edu>
Subject   st: -textbarplot- available from SSC
Date   Thu, 16 Mar 2006 21:34:03 -0000

A few days ago, I mentioned a program -textbarplot- I was
developing. This mention was in response to a posting by  Hiroshi 
Maeda. Austin Nichols contributed helpfully to discussion.

My own earlier stimulus came from teaching. A student had a
reasonable question and the Stata answer was rather complicated 
compared with what she wanted. This is no criticism of -graph bar- or 
-twoway bar-, the main alternatives for doing it: both are general, 
flexible and to that extent necessarily formidable in total. 

Thanks to Kit Baum, this program is now available from 
SSC. Stata 8.2 is required. 	

The major point is best illustrated by example. On a happy holiday
in Stockholm I naturally visited a good bookshop and
acquired a simple statistical guide to Sweden. 

The following data on home access to internet 2002 (%) come
from Statistiska centralbyrån. 2003.  Sweden
in figures/Sverige i siffror 2004. p.52:

        Men                     66.7
        Women                   60.3
                
        16-24                   75.5
        25-34                   75.0
        35-44                   80.0
        45-54                   75.4
        55-64                   59.9
        65-74                   29.8
        75-84                   10.3
                
        Labourers               49.9
        Lower white collar      60.8
        Managers and officials  83.5
        Entrepreneurs           66.3
        Farmers                 26.8
        Old-age pensioners      22.1

In cases like this the breakdown by sex (certainly) or 
by age or occupation (possibly) is too simple to justify
a graph or even a table in a report, but the three 
together show enough to deserve a graph or table. What
I (and my student with her data (and Hiroshi Maeda too with a similar 
example)) would like to be able to do is insist easily on 
precisely this order and precisely the blank lines specified. 
In effect we want almost an immediate graph command. 

With -textbarplot-, you enter these data as two variables, 
say a string variable -text- and a numeric variable -access-, 
with blank strings and missing numerics in observations 3 and 
11 to indicate blank lines. Then

. label var access "home access to internet (%)"
. textbarplot text access

More generally, -textbarplot- produces a horizontal bar plot 
with text shown to the left of the bars. A textvar specifies 
the text and a barvar, which must be a numeric variable, specifies 
the magnitude of the bars.

By default

1. If textvar is a string variable, then observation numbers are
used to determine row positions for the bars, which are y axis
values on a reversed scale, and its values are used as text.

2. If textvar is a numeric variable with labels, then its
numeric values are used to determine row positions, and its
labels are used as text.

3. If textvar is an integer-valued numeric variable, then its
numeric values are used to determine row positions and are also
shown as text.

These defaults can be over-ridden by specifying an integer-valued y
variable with the -y()- option. In that case there are no constraints
on what textvar is.

textbarplot is a wrapper for -twoway bar- and -twoway scatter-.  Other
kinds of graph can be obtained by using a -recast()- option. The most
useful alternatives are -recast(dot)-, -recast(dropline)- and
-recast(spike)-.

By comparison, similar graphs with -graph hbar- can be a little awkward 
if there are to be gaps between clusters of bars or repeated category names.  
-textbarplot- is implemented in terms of -twoway- to provide a simpler 
alternative for some kinds of plots.

In short, -textbarplot- is at best a convenience command, but 
convenience is still preferable to its opposite. 

P.S. There is a -vertical- option to yield giraffe graphics. It's usually a 
bad idea, but you can do it. 

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


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