R Under development (unstable) (2023-08-12 r84939 ucrt) -- "Unsuffered Consequences"
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> options(na.action=na.exclude)  #preserve length of missings
> library(survival)
> 
> #
> # Check out using a "user specified" distribution
> #
> mydist <- c(survreg.distributions$extreme, survreg.distributions$weibull[-1])
> mydist$name <- "Weibull2"
> mydist$dist <- NULL
> 
> fit1 <- survreg(Surv(time, status) ~ age + ph.ecog, lung)
> fit2 <- survreg(Surv(time, status) ~ age + ph.ecog, lung, dist=mydist)
> 
> all.equal(fit1$coef, fit2$coef)
[1] TRUE
> all.equal(fit1$var, fit2$var)
[1] TRUE
> 
> #
> # And with an data set containing interval censoring
> #
> idat <- read.table('data.interval', skip=3, header=T, sep=',')
> 
> fit1 <- survreg(Surv(ltime, rtime, type='interval2') ~ age + ecog.ps, idat)
> fit2 <- survreg(Surv(ltime, rtime, type='interval2') ~ age + ecog.ps, 
+                 data=idat, dist=mydist)
> 
> all.equal(fit1$coef, fit2$coef)
[1] TRUE
> all.equal(fit1$var, fit2$var)
[1] TRUE
> all.equal(fit1$log, fit2$log)
[1] TRUE
> 
> 
> proc.time()
   user  system elapsed 
   0.85    0.09    0.95