Fix edgecolor not set on scatter plots with single-row DataFrame data (#325)

* Initial plan

* Initial analysis of edgecolor issue - found root cause in _from_data function

Co-authored-by: cvanelteren <19485143+cvanelteren@users.noreply.github.com>

* Fix edgecolor issue for scatter plots with single-row DataFrame data

Co-authored-by: cvanelteren <19485143+cvanelteren@users.noreply.github.com>

* Add pytest.mark.mpl_image_compare decorator to test_scatter_edgecolor_single_row

Co-authored-by: cvanelteren <19485143+cvanelteren@users.noreply.github.com>

* Format code with black

Co-authored-by: cvanelteren <19485143+cvanelteren@users.noreply.github.com>

---------

Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>
Co-authored-by: cvanelteren <19485143+cvanelteren@users.noreply.github.com>

Author: Copilot

ultraplot/internals/inputs.py

@@ -247,6 +247,7 @@ def _from_data(data, *args):
     if data is None:
         return
     args = list(args)
+    found_in_data = False
     for i, arg in enumerate(args):
         if isinstance(arg, str):
             try:
@@ -255,6 +256,13 @@ def _from_data(data, *args):
                 pass
             else:
                 args[i] = array
+                found_in_data = True
+
+    # If only one argument and it wasn't found in data, return the original scalar
+    # This prevents scalar values like "none" from becoming ["none"]
+    if len(args) == 1 and not found_in_data:
+        return args[0]
+
     return args
 
 

ultraplot/tests/test_1dplots.py

@@ -295,6 +295,46 @@ def test_scatter_args(rng):
     return fig
 
 
+@pytest.mark.mpl_image_compare
+def test_scatter_edgecolor_single_row():
+    """
+    Test that edgecolor is properly handled for single-row DataFrame input.
+    This is a regression test for issue #324.
+    """
+    import pandas as pd
+
+    # Create test data
+    df_multi = pd.DataFrame({"x": [1, 2], "y": [1, 2], "sizes": [300, 300]})
+    df_single = pd.DataFrame({"x": [2], "y": [2], "sizes": [300]})
+
+    fig, axs = uplt.subplots(ncols=3, share=0)
+
+    # Test multiple rows with alpha
+    result1 = axs[0].scatter(
+        "x", "y", s="sizes", data=df_multi, fc="red8", ec="none", alpha=1
+    )
+
+    # Test single row with alpha (the problematic case)
+    result2 = axs[1].scatter(
+        "x", "y", s="sizes", data=df_single, fc="red8", ec="none", alpha=1
+    )
+
+    # Test single row without alpha
+    result3 = axs[2].scatter("x", "y", s="sizes", data=df_single, fc="red8", ec="none")
+
+    # Verify that edgecolors are correctly set to no edges for all cases
+    # An empty array means no edges (which is what 'none' should produce)
+    assert len(result1.get_edgecolors()) == 0, "Multiple rows should have no edges"
+    assert (
+        len(result2.get_edgecolors()) == 0
+    ), "Single row with alpha should have no edges"
+    assert (
+        len(result3.get_edgecolors()) == 0
+    ), "Single row without alpha should have no edges"
+
+    return fig
+
+
 @pytest.mark.mpl_image_compare
 def test_scatter_inbounds():
     """