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st: RE: adding line y=x

From   "Nick Cox" <>
To   <>
Subject   st: RE: adding line y=x
Date   Fri, 25 Jun 2010 14:14:28 +0100

su var1, meanonly 
twoway (scatter var2 var1, ytitle(`: var label var2') 
xtitle(`: var label var1')) (function equality = x, ra(0 `=r(max)')) 

-twoway function- is odd. -x- is a placeholder for the x-axis variable.
I tend to use some nonce name for the y variable like "equality" because
that then becomes the legend default. 


Jeph Herrin

Is there an easier way to do this? I am trying to
add the canonical line y=x to a twoway scatter plot
of -var2- vs -var1-; here's the briefest approach:

   twoway (scatter var2 var1) (line var2 var2)

The biggest problem with this is that -var1- and -var2- range
from about 2 up to 20, whereas I'd like my line to extend
from the origin (0,0). To do that, I have to add an observation
which contains the origin, and then arrange things so that
the observation is excluded from the scatter plot. The other
problems stem from overlaying two graphs, which means that
for example I have to fiddle with the labelling on the yaxis,
because -twoway- doesn't give precedence to the -scatter- plot.

Is there not a simpler way to simply add the diagonal to
a scatter plot? If not, I would suggest that this would be
a useful feature, much like -yline(), -xline(), and -tline()-
which add vertical and horizontal lines.

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