Merge pull request #312 from jdblischak/event_diff

Define event_diff() as a separate internal function

DESCRIPTION

@@ -1,6 +1,6 @@
 Package: gsDesign2
 Title: Group Sequential Design with Non-Constant Effect
-Version: 1.1.0.3
+Version: 1.1.0.4
 Authors@R: c(
     person("Keaven", "Anderson", email = "keaven_anderson@merck.com", role = c("aut")),
     person("Yilong", "Zhang", email = "elong0527@gmail.com", role = c("aut")),

R/expected_time.R

@@ -97,18 +97,10 @@ expected_time <- function(
     stop("expected_time(): the input target_event` should be a positive numer, rather than a vector!")
   }
 
-  # Build a help function ----
-  # find the difference between  `AHR()` and different values of total_duration
-  event_diff <- function(x) {
-    ans <- ahr(
-      enroll_rate = enroll_rate, fail_rate = fail_rate,
-      total_duration = x, ratio = ratio
-    )$event - target_event
-    return(ans)
-  }
-
   # Perform uniroot AHR() over total_duration ----
-  res <- try(uniroot(event_diff, interval))
+  res <- try(
+    uniroot(event_diff, interval, enroll_rate, fail_rate, ratio, target_event)
+  )
 
   if (inherits(res, "try-error")) {
     stop("expected_time(): solution not found!")
@@ -120,3 +112,26 @@ expected_time <- function(
     return(ans)
   }
 }
+
+#' Considering the enrollment rate, failure rate, and randomization ratio,
+#' calculate the difference between the targeted number of events and the
+#' accumulated events at time `x`
+#'
+#' A helper function passed to `uniroot()`
+#'
+#' @param x Duration
+#' @inheritParams expected_time
+#'
+#' @return A single numeric value that represents the difference between the
+#'   expected number of events for the provided duration (`x`) and the targeted
+#'   number of events (`target_event`)
+#'
+#' @keywords internal
+event_diff <- function(x, enroll_rate, fail_rate, ratio, target_event) {
+  expected <- ahr(
+    enroll_rate = enroll_rate, fail_rate = fail_rate,
+    total_duration = x, ratio = ratio
+  )
+  ans <- expected$event - target_event
+  return(ans)
+}