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Re: st: RE: graph command: xline() with by() option

From   Nick Winter <>
Subject   Re: st: RE: graph command: xline() with by() option
Date   Wed, 20 Aug 2008 12:49:48 -0400 the question too quickly to notice the version 7 reference. So consider this an answer to Nick C's "or even in Stata 10."

--Nick W

Nick Cox wrote:

This is a good idea for Stata 8 up, but won't work in Stata 7, which is
what Achille has.
Nick Winter

How about something like this? you would need to choose the value of -top- to be the right height, which might require some experimentation. And you might want to add options to the -pcspike- plots to set the line color, etc.

. gen zero = 0
. gen top = 0.05

. graph twoway histogram stat || pcspike zero lower_es top lower_es || pcspike zero upper_es top upper_es , by(grp)

Nick Cox wrote:

Unfortunately, it is possible to say why this doesn't work. When Stata
sees any references to local macros in commands, it substitutes them
immediately with their contents and then tries to execute the command.
That applies too to references of form
`= <some calculation>'. In short, that is done once only. Thus there
is no way that what you want will be done separately according to the
distinct values of a variable specified in a -by()- option.
Nor can I think of a neat way to do this in Stata 7, or even Stata 10.
I guess you need to produce individual graphs, and then combine them.
-forval- or -foreach- would help.
Achille M. Luongo

I would like to draw a histogram with two vertical lines showing
upper and lower estimates of a statistic for two (or more) groups
the graph command of Stata 7.0.

This is a snippet of the
example dataset:
grp stat lower_es upper_es
1 91 43.45387 60.79625
1 60 43.45387 60.79625
1 87 43.45387 60.79625
1 52 43.45387 60.79625
2 100 79.70421 124.2349
2 60 79.70421 124.2349
2 77 79.70421 124.2349
2 125 79.70421 124.2349

I have already read the existing
post at
a similar topic.

Nevertheless, I can&rsquo;t figure out how to
draw upper and lower estimates with &lsquo;xline()&rsquo; option when
&lsquo;graph&rsquo; command is combined with the &lsquo;by&rsquo;
like that:

graph stat, by(grp)
xline(`=lower_es[_n]' `= upper_es[_n]')
In fact, the graph
command always draw vertical lines in the same position in all the
histograms combined with the by option (I suppose it always draws
lower_es[1] and upper_es[1]).

I considered the possibility to
create histograms using the &lsquo;by&rsquo; clausole like that:

by grp: graph stat, xline(`=lb[_n]' `=ub[_n]') xlab(0
20 to 140)

but I obtained the the same previous result.
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Nicholas Winter                                 434.924.6994 t
Assistant Professor                             434.924.3359 f
Department of Politics         e
University of Virginia w
PO Box 400787, 100 Cabell Hall
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