BUG: Respect na_rep in DataFrame.to_latex() when used with formatters (#9046)

doc/source/whatsnew/v0.25.0.rst

@@ -355,6 +355,9 @@ I/O
 - Improved performance in :meth:`pandas.read_stata` and :class:`pandas.io.stata.StataReader` when converting columns that have missing values (:issue:`25772`)
 - Bug in :func:`read_hdf` not properly closing store after a ``KeyError`` is raised (:issue:`25766`)
 - Bug in ``read_csv`` which would not raise ``ValueError`` if a column index in ``usecols`` was out of bounds (:issue:`25623`)
+- Bug in :meth:`DataFrame.to_latex` that would ignore ``na_rep`` if the ``formatters`` argument was used (:issue:`9046`)
+-
+
 
 Plotting
 ^^^^^^^^

pandas/io/formats/format.py

@@ -1063,7 +1063,10 @@ def get_result_as_array(self):
         """
 
         if self.formatter is not None:
-            return np.array([self.formatter(x) for x in self.values])
+            out = np.array([self.formatter(x) for x in self.values])
+            mask = isna(self.values)
+            out[mask] = self.na_rep
+            return out
 
         if self.fixed_width:
             threshold = get_option("display.chop_threshold")
@@ -1142,7 +1145,8 @@ def format_values_with(float_format):
     def _format_strings(self):
         # shortcut
         if self.formatter is not None:
-            return [self.formatter(x) for x in self.values]
+            return [self.formatter(x) if not isna(x) else self.na_rep
+                    for x in self.values]
 
         return list(self.get_result_as_array())
 

pandas/tests/io/formats/test_to_latex.py

@@ -741,5 +741,22 @@ def test_to_latex_multindex_header(self):
 0 & 1 &  2 &  3 \\
 \bottomrule
 \end{tabular}
+"""
+        assert observed == expected
+
+    def test_to_latex_na_rep_formatters(self):
+        # GH 9046
+        df = pd.DataFrame({'a': [0, 1, 2], 'b': [0.1, None, 0.2]})
+        observed = df.to_latex(
+            formatters={'b': '{:0.4f}'.format}, na_rep='-')
+        expected = r"""\begin{tabular}{lrr}
+\toprule
+{} &  a &      b \\
+\midrule
+0 &  0 & 0.1000 \\
+1 &  1 &      - \\
+2 &  2 & 0.2000 \\
+\bottomrule
+\end{tabular}
 """
         assert observed == expected