Print sample sizes

Author: VisruthSK

R/loo_compare.R

@@ -186,9 +186,15 @@ loo_compare_checks <- function(loos) {
     stop("All inputs should have class 'loo'.", call.=FALSE)
   }
 
-  Ns <- sapply(loos, function(x) nrow(x$pointwise))
-  if (!all(Ns == Ns[1L])) {
-    stop("Not all models have the same number of data points.", call.=FALSE)
+  Ns <- vapply(loos, function(x) nrow(x$pointwise), integer(1))
+  if (any(Ns != Ns[1L])) {
+    stop(
+      paste0(
+        "All models must have the same number of observations, but models have inconsistent observation counts: ",
+        paste(paste0("'", find_model_names(loos), "' (", Ns, ")"), collapse = ", ")
+      ), 
+      call. = FALSE
+    )
   }
 
   ## warnings

tests/testthat/test_compare.R

@@ -18,8 +18,16 @@ test_that("loo_compare throws appropriate errors", {
   expect_error(loo_compare(w1, list(1, 2, 3)), "class 'loo'")
   expect_error(loo_compare(w1), "requires at least two models")
   expect_error(loo_compare(x = list(w1)), "requires at least two models")
-  expect_error(loo_compare(w1, w3), "same number of data points")
-  expect_error(loo_compare(w1, w2, w3), "same number of data points")
+  expect_error(
+    loo_compare(w1, w3),
+    "All models must have the same number of observations, but models have inconsistent observation counts: 'model1' (32), 'model2' (31)",
+    fixed = TRUE
+  )
+  expect_error(
+    loo_compare(w1, w2, w3),
+    "All models must have the same number of observations, but models have inconsistent observation counts: 'model1' (32), 'model2' (32), 'model3' (31)",
+    fixed = TRUE
+  )
 })
 
 test_that("loo_compare throws appropriate warnings", {