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Re: st: Additional lines on histogram


From   "Eric G. Wruck" <ewruck@econalytics.com>
To   statalist@hsphsun2.harvard.edu
Subject   Re: st: Additional lines on histogram
Date   Fri, 18 Nov 2005 11:27:53 -0500

Very nice -- thank you!

Eric


>Eric G. Wruck <ewruck@econalytics.com> asks,
>
>> I am generating a histogram but want to superimpose additional lines
>> for certain values on the x-axis.  However, the additional line is
>> basically hidden behind one of the histogram bars, only appearing
>> from the top of the bar to the top of the graph.  Is there a way to
>> bring the additional line to the top so that it is drawn on top of
>> the histogram?
>
>I assume that Eric is using the -xline()- option to specify his vertical
>lines.  If so, those lines are "laid down" before the histogram bars are drawn
>and are therefore occluded by the bars.  In many (most?) cases this is what
>you want -- your plots placed atop the vertical (or horizontal reference
>lines).
>
>The position of the -xlines()- cannot be changed, but not to worry.
>-histogram- supports the -addplot()- option, so we can add any -twoway- plot
>to our histogram, and because those plots will be drawn after the histogram
>bars, they will overlay the bars.
>
>Here is a simple example using the auto data set.
>
>      . sysuse auto
>      . hist mpg, addplot(pci 0 20 .1 20)
>
>In the -addplot()- option, we specified the immediate form of the parallel
>coordinates plot, -pci-.  (We could have used other plottypes, but this seemed
>easiest.)  With the 2 supplied coordinates, we are just connecting the line
>from the point (y=0,x=20) to (y=.1,x=20) -- a vertical line at x=20.  I had
>already peeked at the histogram and seen that the y-axis ranged from 0 to .1.
>
>If Eric wants more vertical lines, he can just add more sets of coordinates.
>Eric may also want to add the option -legend(off)- because -histogram- assumes
>that you want each of your plots identified, and I doubt that Eric does.
>
>Note that if we add more coordinates pairs, each line will be drawn in the
>same style -- color, thickness, and pattern.  All of the lines are a single
>plot and thus share a style.  A little-known feature of -addplot()- is that
>you can add more than one plot and thus draw plots with different styles.
>Just separate the plots with a -||- as you would on the -twoway- command.
>Expanding on our example,
>
>      . hist mpg, addplot(pci 0 20 .1 20 0 30 .1 30 || pci 0 25 .1 25)
>
>Draws vertical lines at 20 and at 30 with a common style, and another line at
>25 (from the second -pci-) with a different style.  We can also change the
>look of any of the plots using the standard -lcolor()-, -lwidth()-, and
>-lpattern()- options allowed on all -pci- plots.
>
>We can even add plots of a different type, say labeled marker symbols, by
>adding something like -|| scatteri .05 35 "my text"- after the last -pci-
>specification.
>
>-- Vince
>   vwiggins@stata.com
>


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