Fix test and improve messages

r/R/dplyr-slice.R

@@ -108,7 +108,7 @@ slice_sample.arrow_dplyr_query <- function(.data,
   # If we want n rows sampled, we have to convert n to prop, oversample some
   # just to make sure we get enough, then head(n)
   sampling_n <- missing(prop)
-  if (missing(prop)) {
+  if (sampling_n) {
     prop <- min(n_to_prop(.data, n) + .05, 1)
   }
   validate_prop(prop)
@@ -137,22 +137,22 @@ slice_sample.Dataset <- slice_sample.ArrowTabular <- slice_sample.RecordBatchRea
 prop_to_n <- function(.data, prop) {
   nrows <- nrow(.data)
   if (is.na(nrows)) {
-    arrow_not_supported("Slicing with `prop` when `nrow()` requires evaluating the query")
+    arrow_not_supported("Slicing with `prop` when the query has joins or aggregations")
   }
   validate_prop(prop)
   nrows * prop
 }
 
 validate_prop <- function(prop) {
   if (!is.numeric(prop) || length(prop) != 1 || is.na(prop) || prop < 0 || prop > 1) {
-    stop("`prop` must be a single numeric value in [0, 1]", call. = FALSE)
+    stop("`prop` must be a single numeric value between 0 and 1", call. = FALSE)
   }
 }
 
 n_to_prop <- function(.data, n) {
   nrows <- nrow(.data)
   if (is.na(nrows)) {
-    arrow_not_supported("slice_sample() with `n` when `nrow()` requires evaluating the query")
+    arrow_not_supported("slice_sample() with `n` when the query has joins or aggregations")
   }
   n / nrows
 }

r/tests/testthat/test-dplyr-slice.R

@@ -113,15 +113,15 @@ test_that("slice_sample, ungrouped", {
   # With a larger dataset, we would be more confident to get exactly n
   # but with this dataset, we should at least not get >n rows
   sampled_n <- tab %>%
-    slice_sample(prop = .2) %>%
+    slice_sample(n = 2) %>%
     collect() %>%
     nrow()
   expect_lte(sampled_n, 2)
 
   # Test with dataset, which matters for the UDF HACK
   sampled_n <- tab %>%
     InMemoryDataset$create() %>%
-    slice_sample(prop = .2) %>%
+    slice_sample(n = 2) %>%
     collect() %>%
     nrow()
   expect_lte(sampled_n, 2)
@@ -158,7 +158,7 @@ test_that("input validation", {
   for (p in list("a", -1, 2, c(.01, .02), NA_real_)) {
     expect_error(
       slice_head(tab, prop = !!p),
-      "`prop` must be a single numeric value in [0, 1]",
+      "`prop` must be a single numeric value between 0 and 1",
       fixed = TRUE
     )
   }