Fix px.ecdf counting missing values as observations

CHANGELOG.md

@@ -22,6 +22,7 @@ This project adheres to [Semantic Versioning](http://semver.org/).
 - Fix `px.sunburst`, `px.treemap` and `px.icicle` listing sectors in a different order on every run when `path` is used with a Polars DataFrame; sectors now follow their order of first appearance for all dataframe backends [[#5766](https://github.com/plotly/plotly.py/pull/5766)], with thanks to @Irahan2 for the contribution!
 - Fix `mpl_to_plotly` conversion of matplotlib contour lines and line collections: close contour rings ending with `Z` codes, support dash styles, convert date x-axes, separate disjoint subpaths with `None` separators, hide line collection traces from the legend by default, and group consecutive same-style lines into single traces [[#5770](https://github.com/plotly/plotly.py/pull/5770)], with thanks to @robertoffmoura for the contribution!
 - Fix serialization of box/lasso select data for figures with multiple subplots [[#5710](https://github.com/plotly/plotly.py/pull/5710)], with thanks to @flpi-sun for the contribution!
+- Fix `px.ecdf` counting rows with a missing value as observations, so the curve no longer stops short of 1 (or 100%) and no longer adds a point at a missing x [[#5842](https://github.com/plotly/plotly.py/pull/5842)]
 
 ## [7.1.0] - 2026-09-15
 

plotly/express/_core.py

@@ -2710,6 +2710,8 @@ def make_figure(args, constructor, trace_patch=None, layout_patch=None):
                 base = args["x"] if args["orientation"] == "v" else args["y"]
                 var = args["x"] if args["orientation"] == "h" else args["y"]
                 ascending = args.get("ecdfmode", "standard") != "reversed"
+                # missing values are not observations: exclude them from the ECDF
+                group = group.filter(~nw.col(base).is_null())
                 group = group.sort(by=base, descending=not ascending, nulls_last=True)
                 group_sum = group.get_column(
                     var

tests/test_optional/test_px/test_px_functions.py

@@ -688,3 +688,20 @@ def test_empty_histogram():
     fig = px.histogram()
     assert len(fig.data) == 1
     assert fig.data[0].type == "histogram"
+
+
+@pytest.mark.parametrize(
+    "ecdfmode,expected",
+    [
+        ("standard", [1 / 3, 2 / 3, 1]),
+        ("complementary", [2 / 3, 1 / 3, 0]),
+        ("reversed", [1, 2 / 3, 1 / 3]),
+    ],
+)
+def test_ecdf_ignores_missing_values(constructor, ecdfmode, expected):
+    # a missing value is not an observation: it must not count towards the total
+    # or produce a point of its own
+    data = constructor({"value": [3.0, 1.0, 2.0, None]})
+    fig = px.ecdf(data, x="value", ecdfmode=ecdfmode)
+    assert_array_equal(fig.data[0].x, [1.0, 2.0, 3.0])
+    assert np.allclose(fig.data[0].y, expected)