Jean-Benoit Hardouin <[email protected]> asks:
> I search to display in a biplot graph (obtained with -biplot- under
> Stata 9) the labels instead of the names of the variables. Is it
> possible ? I have not found any help in the manual about that.
Assuming the variable labels were reasonably short and more
descriptive than the variable names, it seems a reasonable thing
to want.
My first guess came from looking at -help biplot- and looking at
the -colopts()- option which allows pcarrow_options as suboptions
(which in turn allow for marker_label_options -- see help
marker_label_options). From this I see that I can ask for a
change in the default size of the labels with
. biplot ... , colopts(mlabsize(huge))
(which produces "huge" labels) and I could change the color, the
gap, the position, etc. The suboption I had hoped would be of
help was
colopts(mlabel(...))
where I would create a variable before calling -biplot- that
contained the variable labels and pass that in through
-colopts(mlabel())-. but the -mlabel()- suboption is not allowed
in the -colopts()- option of -biplot-.
The reason is that Stata's -graph- system thinks in terms of
observations, and the information of the variables (columns) in
-biplot- has to be handled in a special way. -biplot- hijacks
the -mlabel()- option to accomplish the task.
Assuming that seeing the variable names in your graphs is
sufficient for your initial explorations using -biplot- and that
the variable labels are only needed when you are producing your
final biplot (for publication), here is what I would do.
I use the auto dataset as a quick example
sysuse auto
biplot turn trunk mpg
Assuming that this graph is what I want except that I want to
replace "turn", "trunk", and "mpg" in the graph with "Turning
Circle", "Trunk space", and "Mileage" (wording similar to what is
in the variable labels for these 3 variables) I would look at the
y and x locations where the labels should land in the graph and
use that information to directly place the text using the
-text()- option (see twoway_options and follow that to
added_text_option) while suppressing the default labels with the
-colopts(nolabel)- option.
biplot turn trunk mpg, colopts(nolabel) text(0.3 -4.5
"Turning Circle" -5 -4.5 "Trunk space" -3.4 5 "Mileage")
(treat the 2 lines above as one line.)
If you are needing to do this a lot you might want to write a
wrapper command that will take care of a lot of this for you
automatically. Here is a beginning draft of such a command:
=================== begin of biplotvlab.ado =========================
*! version 1.0.0 29sep2005
program biplotvlab
version 9
syntax varlist(numeric min=2) [if] [in] [, *]
// run biplot quietly (and nograph) so we can get r(V)
qui biplot `varlist' `if' `in' , `options' nograph
tempname V
mat `V' = r(V)
// build the -text()- option
local topt "text("
local i 0
foreach v of local varlist {
local ++i
// y value
local topt `"`topt' `= `V'[`i',2]'"'
// x value
local topt `"`topt' `= `V'[`i',1]'"'
// variable label
local topt `"`topt' `"`: var label `v''"' "'
}
local topt `"`topt')"'
// call with -colopts(nolabel)- and -text()- just built
biplot `varlist' `if' `in', `options' colopts(nolabel) `topt'
end
===================== end of biplotvlab.ado =========================
Then I would call this as follows
biplotvlab turn trunk mpg
Notice that -biplotvlab- places the variable labels right on the
ends of the arrows. You probably want to add logic to the code
for moving them out a bit from the ends of the arrows. If so,
replace the
`= `V'[`i',2]' and `= `V'[`i',1]'
with more elaborate code.
If anyone wants to take over this code and enhance it, that is
fine with me. I just wanted to point out the beginning direction
for a solution.
Ken Higbee [email protected]
StataCorp 1-800-STATAPC
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