[R] Survival Plots by Strata

[Bret Collier]

All,
I am struggling to create a survival plot using LTRC data for each year
of a 10 year period.

I have a set of individuals (birds) where 'entry' is the day of the
year (1-365) they are released (let out of pens) into the wild (2 year
data snip below).  'Entry'  (e.g., day of year the first bird is
released for each year) is highly variable, ranging from 48 to >250. 
When I create a plot using the below code I would like to remove the
'solid' line which represent S_hat=1 out to the LC point for each year
and instead have the survival curves formatted in more of a 'hanging'
style, where the LC day (e.g., min(Entry for each year)) is where each
curve begins at S_hat=1 for each year (and does not extend back to the
y-axis)?  I could not find anything on this in the archives or MASS or
Survival Analysis using S?  Anyone have a suggestion on where to look?

TIA, Bret


#Code snip for R email.
apc.coxfit1<-coxph(Surv(Entry, Exit, Fate)~Sex + Agerelease +
Dayrelease + strata(Year), data=mydat)
coxfit.apc<-survfit(apc.coxfit1)
coxfit.apc
plot(survfit(apc.coxfit1), conf.int=F, log=T, lty=c(1:2), col=c(1:2),
xlim=c(205, 800)) #not run--first entry for this example is day 205 for
1996, 259 for 1997

>mydat
ID	Year	Dayrelease
Agerelease	Survivorship	Entry	Exit	Fate	Sex
16240	1996	205	95	164	205	369	1	0
16319	1996	205	88	140	205	345	1	0
16378	1996	248	108	100	248	348	1	0
20383	1996	241	98	204	241	445	1	0
16324	1996	219	90	227	219	446	1	0
16327	1996	219	90	497	219	716	1	0
20373	1996	241	114	413	241	654	1	0
20374	1996	241	111	211	241	452	1	0
16241	1996	205	95	234	205	439	1	1
16321	1996	219	90	118	219	337	1	1
16323	1996	219	90	180	219	399	1	1
20375	1996	241	103	268	241	509	1	1
20384	1996	241	98	299	241	540	1	1
20390	1996	241	93	204	241	445	1	1
20393	1996	241	88	208	241	449	1	1
16313	1996	248	122	512	248	760	0	1
20378	1996	241	103	236	241	477	0	1
20381	1996	241	101	329	241	570	0	1
16328	1996	219	90	224	219	443	0	1
16827	1997	259	127	52	259	311	1	0
16828	1997	259	127	216	259	475	1	0
16831	1997	303	171	19	303	322	1	0
20466	1997	289	149	31	289	320	1	0
20469	1997	289	149	199	289	488	1	0
20483	1997	289	134	18	289	307	1	0
16807	1997	259	137	223	259	482	1	0
16809	1997	259	137	1	259	260	1	0
16819	1997	259	131	237	259	496	1	0
16829	1997	303	171	7	303	310	1	0
20440	1997	289	161	7	289	296	1	0
20470	1997	289	148	257	289	546	1	0
20478	1997	289	143	12	289	301	1	0
16817	1997	259	130	85	259	344	1	0
20454	1997	289	154	4	289	293	1	1
20459	1997	289	153	335	289	624	1	1
20460	1997	289	153	118	289	407	1	1
20465	1997	289	150	31	289	320	1	1
20473	1997	289	147	65	289	354	1	1
20484	1997	289	133	58	289	347	1	1
20489	1997	289	130	56	289	345	1	1
16808	1997	259	137	137	259	396	0	1
16810	1997	303	181	64	303	367	0	1
16816	1997	259	130	1	259	260	0	1
20471	1997	289	147	334	289	623	0	1
16826	1997	259	127	20	259	279	0	1