Add an example to calculate expected events for multiple strata

R/expected_event.R

@@ -107,6 +107,22 @@
 #'   fail_rate = define_fail_rate(duration = 100, fail_rate = log(2) / 6, dropout_rate = .01),
 #'   total_duration = 22, simple = FALSE
 #' )
+#'
+#' # Single time period example, multiple strata
+#' enroll_rate <- define_enroll_rate(stratum = rep(c("Biomarker-positive", "Biomarker-negative"), each = 4),
+#'                                   duration = c(2, 2, 2, 6, 2, 2, 2, 6),
+#'                                   rate = c(1:4, 1:4))
+#' failure_rate <- define_fail_rate(stratum = rep(c("Biomarker-positive", "Biomarker-negative"), each = 2),
+#'                                  duration = c(3, 100, 3, 100),
+#'                                  fail_rate = log(2) / c(8, 12, 8, 10),
+#'                                  dropout_rate = 0.001)
+#' # Total number of expected events
+#' sapply(c("Biomarker-positive", "Biomarker-negative"),
+#'        function(ss){
+#'          expected_event(enroll_rate = enroll_rate[enroll_rate$stratum == ss, ],
+#'                         fail_rate = failure_rate[failure_rate$stratum == ss, ],
+#'                         total_duration = 36,
+#'                         simple = TRUE)}) |> sum()
 expected_event <- function(
     enroll_rate = define_enroll_rate(
       duration = c(2, 2, 10),
@@ -120,6 +136,9 @@ expected_event <- function(
     total_duration = 25,
     simple = TRUE) {
 
+  # Report error where there is >=2 strata
+  if(length(unique(fail_rate$stratum)) >= 2) {stop("Please calculate the expected event by stratum, see examples. ")}
+
   # Divide the time line into sub-intervals ----
 
   ## by piecewise enrollment rates