From f1860abd040ae0534b8c26a4e39abab934f2b477 Mon Sep 17 00:00:00 2001
From: Martin Stancsics <martin.stancsics@quantco.com>
Date: Thu, 29 Jun 2023 14:32:41 +0200
Subject: [PATCH 1/2] Improve the performance of `from_pandas`

---
 CHANGELOG.rst             |  7 +++++++
 src/tabmat/constructor.py | 12 ++----------
 2 files changed, 9 insertions(+), 10 deletions(-)

diff --git a/CHANGELOG.rst b/CHANGELOG.rst
index 83c8aceb..b9d1c5cc 100644
--- a/CHANGELOG.rst
+++ b/CHANGELOG.rst
@@ -7,6 +7,13 @@
 Changelog
 =========
 
+3.1.11 - 2023-XX-XX
+-------------------
+
+**Other changes:**
+
+- Improve the performance of ``from_pandas`` in the case of low-cardinality categorical variables.
+
 3.1.10 - 2023-06-23
 -------------------
 
diff --git a/src/tabmat/constructor.py b/src/tabmat/constructor.py
index b782f2da..f8e23c31 100644
--- a/src/tabmat/constructor.py
+++ b/src/tabmat/constructor.py
@@ -72,6 +72,7 @@ def from_pandas(
         if object_as_cat and coldata.dtype == object:
             coldata = coldata.astype("category")
         if isinstance(coldata.dtype, pd.CategoricalDtype):
+            cat = CategoricalMatrix(coldata, drop_first=drop_first, dtype=dtype)
             if len(coldata.cat.categories) < cat_threshold:
                 (
                     X_dense_F,
@@ -79,15 +80,7 @@ def from_pandas(
                     dense_indices,
                     sparse_indices,
                 ) = _split_sparse_and_dense_parts(
-                    pd.get_dummies(
-                        coldata,
-                        prefix=colname,
-                        sparse=True,
-                        drop_first=drop_first,
-                        dtype=np.float64,
-                    )
-                    .sparse.to_coo()
-                    .tocsc(),
+                    sps.csc_matrix(cat.tocsr(), dtype=dtype),
                     threshold=sparse_threshold,
                 )
                 matrices.append(X_dense_F)
@@ -103,7 +96,6 @@ def from_pandas(
                     indices.append(sparse_indices)
 
             else:
-                cat = CategoricalMatrix(coldata, drop_first=drop_first, dtype=dtype)
                 matrices.append(cat)
                 is_cat.append(True)
                 if cat_position == "expand":

From 2a3bcad3e79f90a4fb2ed57a48774c6e290a3eca Mon Sep 17 00:00:00 2001
From: Martin Stancsics <martin.stancsics@quantco.com>
Date: Tue, 18 Jul 2023 17:50:41 +0200
Subject: [PATCH 2/2] Update changelog according to review

---
 CHANGELOG.rst | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/CHANGELOG.rst b/CHANGELOG.rst
index b9d1c5cc..331695b1 100644
--- a/CHANGELOG.rst
+++ b/CHANGELOG.rst
@@ -7,8 +7,8 @@
 Changelog
 =========
 
-3.1.11 - 2023-XX-XX
--------------------
+Unreleased
+----------
 
 **Other changes:**