fix: nested null data type Series treated as an empty Series (#1023)

NEWS.md

@@ -14,7 +14,7 @@
 ### Other breaking changes
 
 - R objects inside an R list are now converted to Polars data types via
-  `as_polars_series()` (#1021, #1022). For example, up to polars 0.15.1,
+  `as_polars_series()` (#1021, #1022, #1023). For example, up to polars 0.15.1,
   a list containing a data.frame with a column of `{clock}` naive-time class
   was converted to a nested List type of Float64:
 

R/as_polars.R

@@ -319,9 +319,12 @@ as_polars_lf.RPolarsLazyGroupBy = function(x, ...) {
 #'
 #' as_polars_series(data.frame(a = 1:4))
 #'
-#' as_polars_series(pl$Series(1:4, name = "foo"))
+#' as_polars_series(as_polars_series(1:4, name = "foo"))
 #'
 #' as_polars_series(pl$lit(1:4))
+#'
+#' # Nested type support
+#' as_polars_series(list(data.frame(a = I(list(1:4)))))
 as_polars_series = function(x, name = NULL, ...) {
   UseMethod("as_polars_series")
 }
@@ -525,7 +528,6 @@ as_polars_series.clock_zoned_time = function(x, name = NULL, ...) {
 }
 
 
-# TODO: rewrite `recursive_robjname2series_tree` in Rust side
 #' @rdname as_polars_series
 #' @export
 as_polars_series.list = function(x, name = NULL, ...) {

src/rust/src/conversion_r_to_s.rs

@@ -53,11 +53,18 @@ fn recursive_robjname2series_tree(x: &Robj, name: &str) -> pl::PolarsResult<Seri
 
     // handle any supported Robj
     let series_result = match rtype {
+        Rtype::Null => Ok(SeriesTree::SeriesEmptyVec), // flag NULL with this enum, to resolve polars type later
+
         Rtype::ExternalPtr => match () {
             _ if x.inherits("RPolarsSeries") => {
                 let s: RPolarsSeries =
                     unsafe { &mut *x.external_ptr_addr::<RPolarsSeries>() }.clone();
-                Ok(SeriesTree::Series(s.0))
+
+                let dtype = s.0.dtype().clone();
+                match dtype {
+                    pl::DataType::Null => Ok(SeriesTree::SeriesEmptyVec),
+                    _ => Ok(SeriesTree::Series(s.0)),
+                }
             }
             _ => Err(pl::PolarsError::InvalidOperation(
                 "This externalPtr is currently not supported".into(),
@@ -145,8 +152,6 @@ fn recursive_robjname2series_tree(x: &Robj, name: &str) -> pl::PolarsResult<Seri
             Ok(SeriesTree::Series(s))
         }
 
-        Rtype::Null => Ok(SeriesTree::SeriesEmptyVec), // flag NULL with this enum, to resolve polars type later
-
         Rtype::Raw => {
             let rpolars_raw_list = list!(x)
                 .set_class(["rpolars_raw_list", "list"])

tests/testthat/test-as_polars.R

@@ -438,10 +438,17 @@ test_that("as_polars_series for nested type", {
       list(data.frame(a = I(list(data.frame(b = 1L)))))
     )$dtype == pl$List(pl$Struct(a = pl$List(pl$Struct(b = pl$Int32))))
   )
-
-  # TODO: this shouldn't error
-  expect_grepl_error(
-    as_polars_series(list(as_polars_series(NULL), as_polars_series(1L))),
-    "One element was null and another was i32"
+  expect_true(
+    as_polars_series(list(as_polars_series(NULL), as_polars_series(1L)))$dtype == pl$List(pl$Int32)
+  )
+  expect_true(
+    as_polars_series(list(NULL, list(1, 2)))$equals(
+      as_polars_series(list(list(), list(1, 2)))
+    )
+  )
+  expect_true(
+    as_polars_series(list(as_polars_series(NULL), list(1, 2)))$equals(
+      as_polars_series(list(list(), list(1, 2)))
+    )
   )
 })