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Re: st: Re: Reducing number of labels on bar graph


From   vwiggins@stata.com (Vince Wiggins, StataCorp)
To   statalist@hsphsun2.harvard.edu
Subject   Re: st: Re: Reducing number of labels on bar graph
Date   Thu, 06 Nov 2003 13:52:02 -0600

David Epstein <de11@columbia.edu> asks about removing the labels from some of
the bars on his bar graph,

> I know this should be easy, but I'm stumped. I'm drawing a (oneway)
> bar graph with 46 different categories. When stata puts them all on
> the x-axis, they run into each other, so I'd like, for instance, to
> only display numbers 1, 6, 11, etc. up to 46. How does one do this?

Friedrich Huebler <huebler@rocketmail.com> suggests that we might be able to
just set some labels to blank and gives the following example,

> . sysuse auto
> . graph bar mpg, over(make)
> . graph bar mpg, over(make, relabel(1 "1" 2 " " 3 " " 4 " " 5 " " 6
>   "6" 7 " " 8 " " 9 " " 10 " " 11 "11" 12 " " 13 " " 14 " " 15 " " 16
>   "16"))

The -relabel()- suboption is not so much specifying a specific label as it is
giving an alternate label to be used in place of the numeric value for the
category that would be shown if there were no label.  Put another way,
-graph bar- is dead set on labeling all bars or none of them.  

With so many categories, it may be preferable to treat the axis as continuous
and use -twoway bar- rather than graph bar.  If David is graphing means and we
assume his variable is -x- and his category variable is -id-, he might try
something like the following,


    . egen xm = mean(x), by(id)
    . sort id
    . twoway bar xm id if id != id[_n-1] , xlabel(1(5)46)

or, even more simply

    . collapse (mean) x, by(id)
    . tw bar xm, xlabel(1(5)46)

In the first case, we leave David's data intact, but must use an if condition
to identify only one observation per group to be graphed.  Note, that we can
use -xlabel()- to control which bars are labeled.  If David likes his bars to
touch the X-axis, as they do in -graph bar-, he can add the option
-plotregion(margin(b 0))-.  He can also use -barwidth(#)- to control the width
of the bars to taste.


-- Vince 
   vwiggins@stata.com

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