Added option to change shrinkage factor

DESCRIPTION

@@ -88,6 +88,7 @@ Collate:
     'defaults.R'
     'external-exports.R'
     'jmpost-package.R'
+    'settings.R'
     'simulations.R'
     'simulations_gsf.R'
     'simulations_os.R'

R/Prior.R

@@ -188,7 +188,8 @@ NULL
 #' @describeIn Prior-Getter-Methods The prior's initial value
 #' @export
 initialValues.Prior <- function(object, ...) {
-    0.5 * object@init + 0.5 * object@sample(1)
+    getOption("jmpost.prior_shrinkage") * object@init +
+        (1 - getOption("jmpost.prior_shrinkage")) * object@sample(1)
 }
 
 

R/settings.R

@@ -0,0 +1,35 @@
+
+
+
+#' jmpost settings
+#'
+#' @description
+#' Define settings that modify the behaviour of the `jmpost` package
+#'
+#' Each of the following are the name of options that can be set via:
+#' ```
+#' options(<option_name> = <value>)
+#' ```
+#'
+#' ## `jmpost.prior_shrinkage`
+#'
+#' Default = `0.5`
+#'
+#' By default all initial values are drawn as random sample from the respective prior
+#' distribution with a shrinkage factor towards the mean. That is:
+#' ```
+#' initial_value = prior_sample * prior_shrinkage + (1 - prior_shrinkage) * prior_mean
+#' ```
+#' This setting controls the shrinkage factor. A value of 0 means no shrinkage (i.e.
+#' pure random draw) whilst a value of 1 means the intial value is just the mean.
+#'
+#' @examples
+#' \dontrun{
+#' options(jmpost.prior_shrinkage = 0.5)
+#' }
+#' @name jmpost-settings
+NULL
+
+if (is.null(getOption("jmpost.prior_shrinkage", default = NULL))) {
+    options("jmpost.prior_shrinkage" = 0.5)
+}

tests/testthat/test-Prior.R

@@ -156,3 +156,33 @@ test_that("show() works for Prior objects", {
     expect_snapshot(print(prior_loglogistic(1, 2)))
     expect_snapshot(print(prior_invgamma(alpha = 1, beta = 2)))
 })
+
+
+test_that("jmpost.prior_shrinkage works as expected", {
+    x <- prior_normal(1, 2)
+    with_mocked_bindings(
+        {
+            options("jmpost.prior_shrinkage" = 0.5)
+            expect_equal(
+                initialValues(x),
+                1 * 0.5 + 4 * 0.5
+            )
+
+            options("jmpost.prior_shrinkage" = 0.9)
+            expect_equal(
+                initialValues(x),
+                1 * 0.9 + 4 * 0.1
+            )
+
+            options("jmpost.prior_shrinkage" = 0.1)
+            expect_equal(
+                initialValues(x),
+                1 * 0.1 + 4 * 0.9
+            )
+
+            ## Reset Shrinkage factor
+            options("jmpost.prior_shrinkage" = 0.1)
+        },
+        local_rnorm = \(...) 4
+    )
+})