fix: bin width < half spread #3646

examples/histogram_binning_options.py

@@ -0,0 +1,50 @@
+"""
+Histogram binning options on data that does not fit the bin size.
+=================================================================
+
+"""
+import pandas as pd
+
+import seaborn as sns
+import matplotlib.pyplot as plt
+
+if __name__ == '__main__':
+    df_round_up = pd.DataFrame({"x": list(range(58))})
+    df_round_down = pd.DataFrame({"x": list(range(52))})
+    n_plots = 4
+
+    fig, ax = plt.subplots(n_plots, 2, figsize=(5 * 2, 5 * n_plots))
+    fig.suptitle("Histogram binning options\nrange(58) and range(52)")
+    fig.tight_layout()
+
+    hist_n_bins_ru = sns.histplot(df_round_up,
+                                  x="x", bins=10, ax=ax[0][0])
+    hist_n_bins_ru.set_title("bins=10")
+    hist_n_bins_rd = sns.histplot(df_round_down,
+                                  x="x", bins=10, ax=ax[0][1])
+    hist_n_bins_rd.set_title("bins=10")
+
+    hist_binwidth_ru = sns.histplot(df_round_up,
+                                    x="x", binwidth=10, ax=ax[1][0])
+    hist_binwidth_ru.set_title("binwidth=10")
+    hist_binwidth_rd = sns.histplot(df_round_down,
+                                    x="x", binwidth=10, ax=ax[1][1])
+    hist_binwidth_rd.set_title("binwidth=10")
+
+    hist_binrange_ru = sns.histplot(df_round_up,
+                                    x="x", binrange=(0, 60), ax=ax[2][0])
+    hist_binrange_ru.set_title("binrange=(0, 60)")
+    hist_binrange_rd = sns.histplot(df_round_down,
+                                    x="x", binrange=(0, 60), ax=ax[2][1])
+    hist_binrange_rd.set_title("binrange=(0, 60)")
+
+    hist_binrange_and_width_ru = sns.histplot(df_round_up,
+                                              x="x", binwidth=10,
+                                              binrange=(0, 60), ax=ax[3][0])
+    hist_binrange_and_width_ru.set_title("bw=10, br=(0, 60)")
+    hist_binrange_and_width_rd = sns.histplot(df_round_down,
+                                              x="x", binwidth=10,
+                                              binrange=(0, 60), ax=ax[3][1])
+    hist_binrange_and_width_rd.set_title("bw=10, br=(0, 60)")
+
+    plt.savefig("output_files/binning_options.svg")

seaborn/_stats/counting.py

@@ -133,7 +133,7 @@ def _define_bin_edges(self, vals, weight, bins, binwidth, binrange, discrete):
             bin_edges = np.arange(start - .5, stop + 1.5)
         else:
             if binwidth is not None:
-                bins = int(round((stop - start) / binwidth))
+                bins = max(int(round((stop - start) / binwidth)), 1)
             bin_edges = np.histogram_bin_edges(vals, bins, binrange, weight)
 
         # TODO warning or cap on too many bins?

tests/conftest.py

@@ -136,6 +136,18 @@ def long_df(rng):
     return df
 
 
+@pytest.fixture
+def mini_bin_df(rng):
+    n = 100
+    df1 = pd.DataFrame({"x": rng.uniform(0, 100, n // 2),
+                        "a": "a",
+                        "b": "x"})
+    df2 = pd.DataFrame({"x": rng.uniform(0, 1, n // 2),
+                        "a": "b",
+                        "b": "y"})
+    return pd.concat([df1, df2])
+
+
 @pytest.fixture
 def long_dict(long_df):
 

tests/test_axisgrid.py

@@ -721,6 +721,10 @@ def test_data_interchange(self, mock_long_df, long_df):
         for ax in g.axes.flat:
             assert len(ax.collections) == 1
 
+    def test_histplot_with_mini_bin(self, mini_bin_df):
+        grid = ag.FacetGrid(mini_bin_df, col='b', col_wrap=2, hue="a")
+        grid.map(histplot, "x", binwidth=10)
+
 
 class TestPairGrid: