# Gehan-Wilcoxon test in R, using survival and NADA packages

library(NADA)

cu <- read.table('cu.txt',header=T)
# cu.txt includes cu= value, cens=TRUE if censored, and group: 1 or 2

# make sure group is a factor
cu$group.f <- as.factor(cu$group)

# combine values and censoring info, and 'flip' to right censored
cu.cen <- Cen(cu$cu,cu$cens)

# print it out
cu.cen

# summary statistics for each group
#  n.b. these use dl when the smallest value is censored.

cenfit(cu.cen~cu$group)

# test equality using Peto-Peto version of Gehan-Wilcoxon
#  cendiff provides a family of tests, indexed by Rho
#  rho = 1, the default, provides the Peto-Peto version of GW
#  this seems to work the best for data with <dl values

cendiff(cu.cen~cu$group)

# MLE methods

cenmle(cu$cu,cu$cens,cu$group.f,dist='gaussian')
# arguments are data, censoring flag, and a group marker
# group marker must be a factor to compare means
# default distribution is lognormal, can override

# a formula interface is broken, at least on my machine.
# cenmle(Cen(cu$cu,cu$cens)~cu$group.f,dist='gaussian')