lcMethodStratify(
  response,
  stratify,
  center = meanNA,
  nClusters = NaN,
  clusterNames = NULL,
  time = getOption("latrend.time"),
  id = getOption("latrend.id"),
  name = "stratify"
)

data(latrendData)
# Stratification based on the mean response level
method <- lcMethodStratify("Y", mean(Y) > 0,
   clusterNames = c("Low", "High"), id = "Id", time = "Time")
model <- latrend(method, latrendData)
summary(model)

# Stratification function
stratfun <- function(trajdata) {
   trajmean <- mean(trajdata$Y)
   factor(trajmean > 1.7,
      levels = c(FALSE, TRUE),
      labels = c("Low", "High"))
}
method <- lcMethodStratify("Y", stratfun, id = "Id", time = "Time")

# Multiple clusters
stratfun3 <- function(trajdata) {
   trajmean <- mean(trajdata$Y)
   cut(trajmean,
      c(-Inf, .5, 2, Inf),
      labels = c("Low", "Medium", "High"))
}
method <- lcMethodStratify("Y", stratfun3, id = "Id", time = "Time")