feat: n_distinct() supports na.rm = TRUE with a single vector arg…

…ument again (#216)

R/backend-dbplyr__duckdb_connection.R

@@ -78,13 +78,22 @@ duckdb_n_distinct <- function(..., na.rm = FALSE) {
   check_dots_unnamed()
 
   if (!identical(na.rm, FALSE)) {
-    stop("Parameter `na.rm = TRUE` in n_distinct() is currently not supported in DuckDB backend.", call. = FALSE)
-  }
+    cols <- list(...)
+
+    # check for more than one vector argument: only one vector is supported
+    # Why not use ROW() as well? Because duckdb's FILTER clause does not support
+    # a windowing context as of now: https://duckdb.org/docs/sql/query_syntax/filter.html
+    if (length(cols) > 1) {
+      stop("n_distinct(): Only one vector argument is currently supported when `na.rm = TRUE`.", call. = FALSE)
+    }
 
-  # https://duckdb.org/docs/sql/data_types/struct.html#creating-structs-with-the-row-function
-  str_struct <- paste0("row(", paste0(list(...), collapse = ", "), ")")
+    return(sql(paste0("COUNT(DISTINCT ", cols[[1]], ")")))
+  } else {
+    # https://duckdb.org/docs/sql/data_types/struct.html#creating-structs-with-the-row-function
+    str_struct <- paste0("row(", paste0(list(...), collapse = ", "), ")")
 
-  sql(paste0("COUNT(DISTINCT ", str_struct, ")"))
+    return(sql(paste0("COUNT(DISTINCT ", str_struct, ")")))
+  }
 }
 
 # Customized translation functions for DuckDB SQL

tests/testthat/test-backend-dbplyr__duckdb_connection.R

@@ -281,6 +281,9 @@ test_that("aggregators translated correctly", {
   expect_equal(translate(n_distinct(x), window = FALSE), sql(r"{COUNT(DISTINCT row(x))}"))
   expect_equal(translate(n_distinct(x), window = TRUE), sql(r"{COUNT(DISTINCT row(x)) OVER ()}"))
   expect_equal(translate(n_distinct(x), window = TRUE, vars_group = "y"), sql(r"{COUNT(DISTINCT row(x)) OVER (PARTITION BY y)}"))
+  expect_equal(translate(n_distinct(x, na.rm = TRUE), window = FALSE), sql(r"{COUNT(DISTINCT x)}"))
+  expect_equal(translate(n_distinct(x, na.rm = TRUE), window = TRUE), sql(r"{COUNT(DISTINCT x) OVER ()}"))
+  expect_equal(translate(n_distinct(x, na.rm = TRUE), window = TRUE, vars_group = "y"), sql(r"{COUNT(DISTINCT x) OVER (PARTITION BY y)}"))
 })
 
 test_that("two variable aggregates are translated correctly", {
@@ -317,8 +320,17 @@ test_that("n_distinct() computations are correct", {
   df <- tbl(con, "df")
   df_na <- tbl(con, "df_na")
 
+  expect_equal(
+    pull(summarize(df, n = n_distinct(x, na.rm = TRUE)), n),
+    2
+  )
+  expect_equal(
+    pull(summarize(df_na, n = n_distinct(x, na.rm = TRUE)), n),
+    2
+  )
+
   expect_error(
-    pull(summarize(df, n = n_distinct(x, na.rm = TRUE)), n)
+    pull(summarize(df, n = n_distinct(x, y, na.rm = TRUE)), n)
   )
 
   # single column is working as usual