Fixes 975 by only removing leftmost array dimension if equal to 1 (#993)

* Fixes 975 by only removing leftmost array dimension if equal to 1

* Update tests, fix windows error

---------

Co-authored-by: Andrew Johnson <andrew.johnson@arjohnsonau.com>

Author: SteveBronder

R/args.R

@@ -1063,6 +1063,24 @@ process_init.default <- function(init, ...) {
   return(init)
 }
 
+#' Remove the leftmost dimension if equal to 1
+#' @noRd
+#' @param x An array like object
+.remove_leftmost_dim <- function(x) {
+  dims <- dim(x)
+  if (length(dims) == 1) {
+    return(drop(x))
+  } else if (dims[1] == 1) {
+    new_dims <- dims[-1]
+    # Create a call to subset the array, maintaining all remaining dimensions
+    subset_expr <- as.call(c(as.name("["), list(x), 1, rep(TRUE, length(new_dims)), drop = FALSE))
+    new_x <- eval(subset_expr)
+    return(array(new_x, dim = new_dims))
+  } else {
+    return(x)
+  }
+}
+
 #' Write initial values to files if provided as posterior `draws` object
 #' @noRd
 #' @param init A type that inherits the `posterior::draws` class.
@@ -1097,9 +1115,13 @@ process_init.draws <- function(init, num_procs, model_variables = NULL,
   draws_rvar <- posterior::subset_draws(draws_rvar, variable = variable_names)
   inits = lapply(1:num_procs, function(draw_iter) {
     init_i = lapply(variable_names, function(var_name) {
-      x = drop(posterior::draws_of(drop(
-        posterior::subset_draws(draws_rvar[[var_name]], draw=draw_iter))))
-      return(x)
+      x = .remove_leftmost_dim(posterior::draws_of(
+        posterior::subset_draws(draws_rvar[[var_name]], draw=draw_iter)))
+      if (model_variables$parameters[[var_name]]$dimensions == 0) {
+        return(as.double(x))
+      } else {
+        return(x)
+      }
     })
     bad_names = unlist(lapply(variable_names, function(var_name) {
       x = drop(posterior::draws_of(drop(
@@ -1295,13 +1317,13 @@ process_init_approx <- function(init, num_procs, model_variables = NULL,
   # Calculate unique draws based on 'lw' using base R functions
   unique_draws = length(unique(draws_df$lw))
   if (num_procs > unique_draws) {
-    if (inherits(init, " CmdStanPathfinder ")) {
+    if (inherits(init, "CmdStanPathfinder")) {
       algo_name = " Pathfinder "
       extra_msg = " Try running Pathfinder with psis_resample=FALSE."
     } else if (inherits(init, "CmdStanVB")) {
       algo_name = " CmdStanVB "
       extra_msg = ""
-    } else if (inherits(init, " CmdStanLaplace ")) {
+    } else if (inherits(init, "CmdStanLaplace")) {
       algo_name = " CmdStanLaplace "
       extra_msg = ""
     } else {

tests/testthat/test-model-init.R

@@ -310,3 +310,28 @@ test_that("Initial values for single-element containers treated correctly", {
     )
   )
 })
+
+test_that("Pathfinder inits do not drop dimensions", {
+  modcode <- "
+  data {
+    int N;
+    vector[N] y;
+  }
+
+  parameters {
+    matrix[N, 1] mu;
+    matrix[1, N] mu_2;
+    vector<lower=0>[N] sigma;
+  }
+
+  model {
+    target += normal_lupdf(y | mu[:, 1], sigma);
+    target += normal_lupdf(y | mu_2[1], sigma);
+  }
+  "
+  mod <- cmdstan_model(write_stan_file(modcode), force_recompile = TRUE)
+  data <- list(N = 100, y = rnorm(100))
+  pf <- mod$pathfinder(data = data, psis_resample = FALSE)
+  expect_no_error(fit <- mod$sample(data = data, init = pf, chains = 1,
+                                    iter_warmup = 100, iter_sampling = 100))
+})