Improve FacetGrid margin titles to not show previous texts (#2083)

* Improve FacetGrid margin titles to not show previous texts

* Add ref to github issue

doc/releases/v0.11.0.txt

@@ -21,3 +21,5 @@ v0.11.0 (Unreleased)
 - Added the ``axes_dict`` attribute to :class:`FacetGrid` for named access to the component axes.  GH2046
 
 - Made :meth:`FacetGrid.set_axis_labels` clear labels from "interior" axes.  GH2046
+
+- Improved :meth:`FacetGrid.set_titles` with `margin titles=True`, such that texts representing the original row titles are removed before adding new ones. GH2083

seaborn/axisgrid.py

@@ -385,6 +385,7 @@ def __init__(
         self._col_var = col
 
         self._margin_titles = margin_titles
+        self._margin_titles_texts = []
         self._col_wrap = col_wrap
         self._hue_var = hue_var
         self._colors = colors
@@ -1005,16 +1006,24 @@ def set_titles(self, template=None, row_template=None, col_template=None,
         template = utils.to_utf8(template)
 
         if self._margin_titles:
+
+            # Remove any existing title texts
+            for text in self._margin_titles_texts:
+                text.remove()
+            self._margin_titles_texts = []
+
             if self.row_names is not None:
                 # Draw the row titles on the right edge of the grid
                 for i, row_name in enumerate(self.row_names):
                     ax = self.axes[i, -1]
                     args.update(dict(row_name=row_name))
                     title = row_template.format(**args)
-                    bgcolor = self.fig.get_facecolor()
-                    ax.annotate(title, xy=(1.02, .5), xycoords="axes fraction",
-                                rotation=270, ha="left", va="center",
-                                backgroundcolor=bgcolor, **kwargs)
+                    text = ax.annotate(
+                        title, xy=(1.02, .5), xycoords="axes fraction",
+                        rotation=270, ha="left", va="center",
+                        **kwargs
+                    )
+                    self._margin_titles_texts.append(text)
 
             if self.col_names is not None:
                 # Draw the column titles  as normal titles

seaborn/tests/test_axisgrid.py

@@ -473,19 +473,23 @@ def test_set_titles_margin_titles(self):
         g.map(plt.plot, "x", "y")
 
         # Test the default titles
-        nt.assert_equal(g.axes[0, 0].get_title(), "b = m")
-        nt.assert_equal(g.axes[0, 1].get_title(), "b = n")
-        nt.assert_equal(g.axes[1, 0].get_title(), "")
+        assert g.axes[0, 0].get_title() == "b = m"
+        assert g.axes[0, 1].get_title() == "b = n"
+        assert g.axes[1, 0].get_title() == ""
 
         # Test the row "titles"
-        nt.assert_equal(g.axes[0, 1].texts[0].get_text(), "a = a")
-        nt.assert_equal(g.axes[1, 1].texts[0].get_text(), "a = b")
-
-        # Test a provided title
-        g.set_titles(col_template="{col_var} == {col_name}")
-        nt.assert_equal(g.axes[0, 0].get_title(), "b == m")
-        nt.assert_equal(g.axes[0, 1].get_title(), "b == n")
-        nt.assert_equal(g.axes[1, 0].get_title(), "")
+        assert g.axes[0, 1].texts[0].get_text() == "a = a"
+        assert g.axes[1, 1].texts[0].get_text() == "a = b"
+        assert g.axes[0, 1].texts[0] is g._margin_titles_texts[0]
+
+        # Test provided titles
+        g.set_titles(col_template="{col_name}", row_template="{row_name}")
+        assert g.axes[0, 0].get_title() == "m"
+        assert g.axes[0, 1].get_title() == "n"
+        assert g.axes[1, 0].get_title() == ""
+
+        assert len(g.axes[1, 1].texts) == 1
+        assert g.axes[1, 1].texts[0].get_text() == "b"
 
     def test_set_ticklabels(self):