st: How to make local condition for graph command

[Caleb Southworth <caleb.southworth@gmail.com>]

This code creates a table and Kaplan Meier graphs for five
event-history outcomes.

My problem is that under some circumstances, the 25th percentile is
undefined, so my -local p25- is undefined. This causes graph to crash
because I cannot specify a line at a missing value. Could someone
propose a work-around that is the logical equivalent of

local p25="" if missing(r(p25))

The crash occurs in the line "sts graph" when missing(r(p25))

begin code:

set more off
log using ${docpath}stdesc.txt, text replace
log off
local mean
local p25
assert event!=.&event<=5
forval i=1/5 {
	qui stset app_dt, fail(event==`i') id(Cin) origin(time td(1Jan2008)) noshow
	qui log on
	qui stdescribe
	di "event= " `i' " subjects= " r(N_sub) " failure= " r(N_fail) "
mean= " r(f_mean)
	qui log off
	qui stci, rmean
	local mean=round(r(rmean))
	qui stci, p(25)
	local p25=round(r(p25))
	sts graph, xline(`p25' `mean') xlab(0(300)1500 `p25' `mean',
angle(45)) saving(${gphpath}km`i'.gph, replace)
	}
log close

Here's the actual crash:

event= 4 subjects= 63399 failure= 696 mean= .01097809
invalid label specifier, :  . 1537:
r(198);

Thanks!

--Caleb.
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