Do not convert columns in the dataset categoricals

closes #913

Author: has2k1

doc/changelog.qmd

@@ -1,6 +1,16 @@
 ---
 title: Changelog
 ---
+## v0.15.0
+
+(not-yet-released)
+
+### Enhancements
+
+- Included datasets [](:attr:`~plotnine.data.mpg`), [](:attr:`~plotnine.data.msleep`) and
+  [](:attr:`~plotnine.data.midwest`) no longer have any of their columns as categoricals.
+  This matches the respective datasets in R. {{< issue 913 >}}
+
 ## v0.14.5
 (2025-01-02)
 [![](https://zenodo.org/badge/DOI/10.5281/zenodo.14587381.svg)](https://doi.org/10.5281/zenodo.14587381)

plotnine/data/__init__.py

@@ -81,7 +81,7 @@ def _process_categories():
     """
     Set columns in some of the dataframes to categoricals
     """
-    global diamonds, midwest, mpg, msleep, penguins
+    global diamonds, penguins
     diamonds = _ordered_categories(
         diamonds,
         {
@@ -90,11 +90,6 @@ def _process_categories():
             "color": list("DEFGHIJ"),
         },
     )
-    mpg = _unordered_categories(
-        mpg, "manufacturer model trans fl drv class".split()
-    )
-    midwest = _unordered_categories(midwest, ["category"])
-    msleep = _unordered_categories(msleep, ["vore", "conservation"])
     penguins = _unordered_categories(penguins, ["species", "island", "sex"])