From 1884881b1cf27a421cdc2dbf6cbe9c207daf9856 Mon Sep 17 00:00:00 2001
From: gepcel <gepcelway@gmail.com>
Date: Fri, 14 Aug 2026 15:41:01 +0800
Subject: [PATCH 1/2] Add kde support for hist

---
 ultraplot/axes/plot.py | 20 ++++++++++++++++++++
 1 file changed, 20 insertions(+)

diff --git a/ultraplot/axes/plot.py b/ultraplot/axes/plot.py
index 6bd62acaf..2a28b6a29 100644
--- a/ultraplot/axes/plot.py
+++ b/ultraplot/axes/plot.py
@@ -7114,6 +7114,8 @@ def _apply_hist(
         filled=None,
         histtype=None,
         orientation="vertical",
+        kde=False,
+        kde_kw=None,
         **kwargs,
     ):
         """
@@ -7157,6 +7159,24 @@ def _apply_hist(
                 if type(sub) is list:
                     res[i] = cbook.silent_list("Polygon", sub)
         self._update_guide(res, **guide_kw)
+        # add kde line
+        if not kde:
+            return obj
+        from scipy.stats import gaussian_kde
+        edges = obj[1]
+        kde_kw = dict(kde_kw or {})
+        density = kw.get('density', False)
+        data2d = xs if xs.ndim > 1 else xs[:, None] # (M, N) data
+        stepsize = kde_kw.pop('stepsize', 300)
+        for i in range(data2d.shape[1]):
+            _x = data2d[:, i]
+            xa = np.linspace(_x.min(), _x.max(), stepsize)
+            ya = gaussian_kde(_x)(xa)
+            if not density:
+                idx = np.clip(np.digitize(xa, edges)-1, 0, len(edges)-2)
+                ya = ya * len(_x) * np.diff(edges)[idx]
+            x_line, y_line = (xa, ya) if orientation=="vertical" else (ya, xa)
+            self._call_native("plot", x_line, y_line, **kde_kw)
         return obj
 
     @inputs._preprocess_or_redirect("x", "bins", keywords="weights")

From d94ea35ae663afa45d2db08624c8029a3a39bbe0 Mon Sep 17 00:00:00 2001
From: gepcel <gepcelway@gmail.com>
Date: Fri, 14 Aug 2026 18:00:27 +0800
Subject: [PATCH 2/2] add some tests

---
 ultraplot/tests/test_1dplots.py | 36 +++++++++++++++++++++++++++++++++
 1 file changed, 36 insertions(+)

diff --git a/ultraplot/tests/test_1dplots.py b/ultraplot/tests/test_1dplots.py
index c04486a12..aa49d603c 100644
--- a/ultraplot/tests/test_1dplots.py
+++ b/ultraplot/tests/test_1dplots.py
@@ -243,6 +243,42 @@ def test_histogram_types(rng):
         ax.hist(data, ec="k", **kw)
     return fig
 
+def test_hist_kde_lines(rng):
+    """
+    Test kde for hist.
+    """
+    data = rng.normal(size=200)
+    # No kde if no kde is not given
+    fig, ax = uplt.subplot()
+    ax.hist(data, bins=20)
+    assert len(ax.lines) == 0
+    # No kde if kde=False
+    ax.hist(data, bins=20, kde=False)
+    assert len(ax.lines) == 0
+    # One kde line with
+    ax.hist(data, bins=20, kde=True)
+    assert len(ax.lines) == 1
+    # test step size
+    line = ax.lines[-1]
+    # default stepsize is 300
+    assert line.get_xdata().size == 300
+    assert line.get_ydata().size == 300
+    assert line.get_xdata()[0] == pytest.approx(data.min())
+    assert line.get_xdata()[-1] == pytest.approx(data.max())
+    # use kde_kw to set stepsize=150
+    ax.hist(data, bins=20, kde=True, density=True, 
+        kde_kw={'stepsize': 150})
+    density_line = ax.lines[-1]
+    assert density_line.get_xdata().size == 150
+    assert density_line.get_ydata().size == 150
+    # test density, default is False, but to to test accurate?    
+    assert line.get_ydata().max() > 1.0
+    assert density_line.get_ydata().max() <= 1.0
+    # test area==1
+    area = np.trapezoid(density_line.get_ydata(), density_line.get_xdata())
+    assert area == pytest.approx(1.0, rel=1e-2)
+    uplt.close(fig)
+
 
 @pytest.mark.mpl_image_compare
 def test_invalid_plot(rng):