Add newdata arg to simulate.sdmTMB()

DESCRIPTION

@@ -1,7 +1,7 @@
 Type: Package
 Package: sdmTMB
 Title: Spatial and Spatiotemporal SPDE-Based GLMMs with 'TMB'
-Version: 0.6.0.9011
+Version: 0.6.0.9012
 Authors@R: c(
     person(c("Sean", "C."), "Anderson", , "[email protected]",
            role = c("aut", "cre"),

NEWS.md

@@ -1,5 +1,12 @@
 # sdmTMB (development version)
 
+* Add `newdata` argument to `simulate.sdmTMB()`. This enables simulating on
+  a new data frame similar to how one would predict on new data.
+
+* Add `mle_mvn_samples` argument to `simulate.sdmTMB()`. Defaults to "single".
+  If "multiple", then a sample from the random effects is taken for each
+  simulation iteration.
+
 * Add `project()` experimental function.
 
 * Add print method for `sdmTMB_cv()` output. #319

R/tmb-sim.R

@@ -332,8 +332,12 @@ sdmTMB_simulate <- function(formula,
 #'   effects (this only simulates observation error). `~0` or `NA` to simulate
 #'   new random affects (smoothers, which internally are random effects, will
 #'   not be simulated as new).
+#' @param mle_mvn_samples Applies if `type = "mle-mvn"`. If `"single"`, take
+#'   a single MVN draw from the random effects. If `"multiple"`, take an MVN
+#'   draw from the random effects for each of the `nsim`.
 #' @param model If a delta/hurdle model, which model to simulate from?
 #'   `NA` = combined, `1` = first model, `2` = second mdoel.
+#' @param newdata Optional new data frame from which to simulate.
 #' @param mcmc_samples An optional matrix of MCMC samples. See `extract_mcmc()`
 #'   in the \href{https://github.com/pbs-assess/sdmTMBextra}{sdmTMBextra}
 #'   package.
@@ -381,10 +385,16 @@ sdmTMB_simulate <- function(formula,
 simulate.sdmTMB <- function(object, nsim = 1L, seed = sample.int(1e6, 1L),
                             type = c("mle-eb", "mle-mvn"),
                             model = c(NA, 1, 2),
-                            re_form = NULL, mcmc_samples = NULL, silent = FALSE, ...) {
+                            newdata = NULL,
+                            re_form = NULL,
+                            mle_mvn_samples = c("single", "multiple"),
+                            mcmc_samples = NULL,
+                            silent = FALSE,
+                            ...) {
   set.seed(seed)
   type <- tolower(type)
   type <- match.arg(type)
+  mle_mvn_samples <- match.arg(mle_mvn_samples)
   assert_that(as.integer(model[[1]]) %in% c(NA_integer_, 1L, 2L))
 
   # need to re-attach environment if in fresh session
@@ -403,6 +413,16 @@ simulate.sdmTMB <- function(object, nsim = 1L, seed = sample.int(1e6, 1L),
     stopifnot(length(object$tmb_data$sim_re) == 6L) # in case this gets changed
     tmb_dat$sim_re <- c(rep(1L, 5L), 0L) # last is smoothers; don't simulate them
   }
+
+  if (!is.null(newdata)) {
+    # generate prediction TMB data list
+    p <- predict(object, newdata = newdata, return_tmb_data = TRUE, ...)
+    # move data elements over
+    p <- move_proj_to_tmbdat(p, object, newdata)
+    p$sim_re <- tmb_dat$sim_re
+    tmb_dat <- p
+  }
+
   newobj <- TMB::MakeADFun(
     data = tmb_dat, map = object$tmb_map,
     random = object$tmb_random, parameters = object$tmb_obj$env$parList(), DLL = "sdmTMB"
@@ -411,9 +431,17 @@ simulate.sdmTMB <- function(object, nsim = 1L, seed = sample.int(1e6, 1L),
   # params MLE/MVN stuff
   if (is.null(mcmc_samples)) {
     if (type == "mle-mvn") {
-      new_par <- .one_sample_posterior(object)
+      if (mle_mvn_samples == "single") {
+        new_par <- .one_sample_posterior(object)
+        new_par <- replicate(nsim, new_par)
+      } else {
+        new_par <- lapply(seq_len(nsim), \(i) .one_sample_posterior(object))
+        new_par <- do.call(cbind, new_par)
+      }
     } else if (type == "mle-eb") {
       new_par <- object$tmb_obj$env$last.par.best
+      new_par <- lapply(seq_len(nsim), \(i) new_par)
+      new_par <- do.call(cbind, new_par)
     } else {
       cli_abort("`type` type not defined")
     }
@@ -432,7 +460,7 @@ simulate.sdmTMB <- function(object, nsim = 1L, seed = sample.int(1e6, 1L),
   } else {
     for (i in seq_len(nsim)) {
       if (!silent) cli::cli_progress_update()
-      ret[[i]] <- newobj$simulate(par = new_par, complete = FALSE)$y_i
+      ret[[i]] <- newobj$simulate(par = new_par[, i, drop = TRUE], complete = FALSE)$y_i
     }
   }
   if (!silent) cli::cli_progress_done()

tests/testthat/test-6-tmb-simulation.R

@@ -180,6 +180,51 @@ test_that("simulate() behaves OK with or without random effects across types", {
   expect_length(s, 969)
 })
 
+test_that("simulate() method works with newdata", {
+  skip_on_cran()
+  fit <- sdmTMB(
+    present ~ 1,
+    time = "year",
+    data = pcod_2011, spatial = "on",
+    spatiotemporal = "iid",
+    family = binomial(),
+    mesh = pcod_mesh_2011
+  )
+  s <- simulate(fit)
+  expect_true(nrow(s) == nrow(pcod_2011))
+  g <- replicate_df(qcs_grid, "year", unique(pcod_2011$year))
+  s <- simulate(fit, newdata = g)
+  expect_true(nrow(s) == nrow(g))
+  s <- simulate(fit, newdata = subset(g, year == 2011))
+  nrow(s)
+  expect_true(nrow(s) == nrow(subset(g, year == 2011)))
+
+  gg <- subset(g, year == 2011)
+  set.seed(1)
+  s <- simulate(fit, newdata = gg, nsim = 400L)
+  a <- apply(s, 1, mean)
+  p <- predict(fit, newdata = gg)
+  plot(a, plogis(p$est))
+  expect_gt(cor(a, plogis(p$est)), 0.98)
+
+  set.seed(1)
+  s1 <- simulate(fit, type = "mle-mvn", mle_mvn_samples = "single", nsim = 100)
+  set.seed(1)
+  s2 <- simulate(fit, type = "mle-mvn", mle_mvn_samples = "multiple", nsim = 100)
+  set.seed(1)
+  s3 <- simulate(fit, type = "mle-eb", nsim = 100)
+
+  expect_false(identical(s1, s2))
+  expect_false(identical(s1, s3))
+
+  sd1 <- apply(s1, 1, sd)
+  sd2 <- apply(s2, 1, sd)
+  sd3 <- apply(s3, 1, sd)
+
+  expect_lt(mean(sd1), mean(sd2))
+})
+
+
 # test_that("TMB Delta simulation works", {
 #   skip_on_cran()
 #   skip_if_not_installed("INLA")