From 96b8b93a959c24ea4c4a5f8aa8c375a167f5699b Mon Sep 17 00:00:00 2001
From: chielP <chielpeters@live.nl>
Date: Fri, 26 Jan 2024 15:14:50 +0100
Subject: [PATCH] fix: Fix casting from categorical to numeric (#13957)

---
 .../chunked_array/logical/categorical/mod.rs    | 17 +++++++++++++++++
 .../tests/unit/datatypes/test_categorical.py    | 12 ++++++++++++
 2 files changed, 29 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 ead8ae6e4271..ba282994de65 100644
--- a/crates/polars-core/src/chunked_array/logical/categorical/mod.rs
+++ b/crates/polars-core/src/chunked_array/logical/categorical/mod.rs
@@ -394,6 +394,23 @@ 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)?;
+
+                #[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) })
+                }
+            },
             _ => 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