From 76350caab2369c61f199f34a4aa51cdf1ca9fee0 Mon Sep 17 00:00:00 2001
From: chielP <chielpeters@live.nl>
Date: Wed, 24 Jan 2024 16:07:17 +0100
Subject: [PATCH 1/2] cat casting

---
 .../chunked_array/logical/categorical/mod.rs  | 21 +++++++++++++++++++
 .../tests/unit/datatypes/test_categorical.py  | 12 +++++++++++
 2 files changed, 33 insertions(+)

diff --git a/crates/polars-core/src/chunked_array/logical/categorical/mod.rs b/crates/polars-core/src/chunked_array/logical/categorical/mod.rs
index 9d79dc28de8a..7eaec38f7201 100644
--- a/crates/polars-core/src/chunked_array/logical/categorical/mod.rs
+++ b/crates/polars-core/src/chunked_array/logical/categorical/mod.rs
@@ -355,6 +355,27 @@ impl LogicalType for CategoricalChunked {
                 // Otherwise we do nothing
                 Ok(self.clone().set_ordering(*ordering, true).into_series())
             },
+            dt if dt.is_numeric() => {
+                // Apply the cast to to the categories and then index into the casted series
+                let categories =
+                    StringChunked::with_chunk("", self.get_rev_map().get_categories().clone());
+                let casted_series = categories.cast(dtype)?;
+
+                macro_rules! get_elements {
+                    ($ca:expr) => {{
+                        Ok(self
+                            .physical()
+                            .into_iter()
+                            .map(|opt_el| {
+                                opt_el.map(|el: u32| unsafe {
+                                    $ca.get_unchecked(el as usize).unwrap()
+                                })
+                            })
+                            .collect())
+                    }};
+                }
+                downcast_as_macro_arg_physical!(casted_series, get_elements)
+            },
             _ => self.physical.cast(dtype),
         }
     }
diff --git a/py-polars/tests/unit/datatypes/test_categorical.py b/py-polars/tests/unit/datatypes/test_categorical.py
index 07f7a2026305..4e02decb8fe9 100644
--- a/py-polars/tests/unit/datatypes/test_categorical.py
+++ b/py-polars/tests/unit/datatypes/test_categorical.py
@@ -800,3 +800,15 @@ def test_sort_categorical_retain_none(
                 "foo",
                 "ham",
             ]
+
+
+def test_cast_from_cat_to_numeric() -> None:
+    cat_series = pl.Series(
+        "cat_series",
+        ["0.69845702", "0.69317475", "2.43642724", "-0.95303469", "0.60684237"],
+    ).cast(pl.Categorical)
+    maximum = cat_series.cast(pl.Float32).max()
+    assert abs(maximum - 2.43642724) < 1e-6  # type: ignore[operator]
+
+    s = pl.Series(["1", "2", "3"], dtype=pl.Categorical)
+    assert s.cast(pl.UInt8).sum() == 6

From 38d2f701f84af9230ba22670cd08b0502e9679fc Mon Sep 17 00:00:00 2001
From: chielP <chielpeters@live.nl>
Date: Fri, 26 Jan 2024 14:15:43 +0100
Subject: [PATCH 2/2] gather

---
 .../chunked_array/logical/categorical/mod.rs  | 22 ++++++++-----------
 1 file changed, 9 insertions(+), 13 deletions(-)

diff --git a/crates/polars-core/src/chunked_array/logical/categorical/mod.rs b/crates/polars-core/src/chunked_array/logical/categorical/mod.rs
index 7eaec38f7201..7b286e476e09 100644
--- a/crates/polars-core/src/chunked_array/logical/categorical/mod.rs
+++ b/crates/polars-core/src/chunked_array/logical/categorical/mod.rs
@@ -361,20 +361,16 @@ impl LogicalType for CategoricalChunked {
                     StringChunked::with_chunk("", self.get_rev_map().get_categories().clone());
                 let casted_series = categories.cast(dtype)?;
 
-                macro_rules! get_elements {
-                    ($ca:expr) => {{
-                        Ok(self
-                            .physical()
-                            .into_iter()
-                            .map(|opt_el| {
-                                opt_el.map(|el: u32| unsafe {
-                                    $ca.get_unchecked(el as usize).unwrap()
-                                })
-                            })
-                            .collect())
-                    }};
+                #[cfg(feature = "bigidx")]
+                {
+                    let s = self.physical.cast(&DataType::UInt64)?;
+                    Ok(unsafe { casted_series.take_unchecked(s.u64()?) })
+                }
+                #[cfg(not(feature = "bigidx"))]
+                {
+                    // Safety: Invariant of categorical means indices are in bound
+                    Ok(unsafe { casted_series.take_unchecked(&self.physical) })
                 }
-                downcast_as_macro_arg_physical!(casted_series, get_elements)
             },
             _ => self.physical.cast(dtype),
         }