BUG: to_string ignoring formatter for FloatingArray (#50333)

Author: phofl

doc/source/whatsnew/v2.0.0.rst

@@ -880,7 +880,8 @@ I/O
 - Bug in :func:`read_sql_query` ignoring ``dtype`` argument when ``chunksize`` is specified and result is empty (:issue:`50245`)
 - Bug in :func:`read_csv` for a single-line csv with fewer columns than ``names`` raised :class:`.errors.ParserError` with ``engine="c"`` (:issue:`47566`)
 - Bug in displaying ``string`` dtypes not showing storage option (:issue:`50099`)
-- Bug in :func:`DataFrame.to_string` with ``header=False`` that printed the index name on the same line as the first row of the data (:issue:`49230`)
+- Bug in :meth:`DataFrame.to_string` with ``header=False`` that printed the index name on the same line as the first row of the data (:issue:`49230`)
+- Bug in :meth:`DataFrame.to_string` ignoring float formatter for extension arrays (:issue:`39336`)
 - Fixed memory leak which stemmed from the initialization of the internal JSON module (:issue:`49222`)
 - Fixed issue where :func:`json_normalize` would incorrectly remove leading characters from column names that matched the ``sep`` argument (:issue:`49861`)
 - Bug in :meth:`DataFrame.to_json` where it would segfault when failing to encode a string (:issue:`50307`)

pandas/io/formats/format.py

@@ -1259,6 +1259,7 @@ def format_array(
     decimal: str = ".",
     leading_space: bool | None = True,
     quoting: int | None = None,
+    fallback_formatter: Callable | None = None,
 ) -> list[str]:
     """
     Format an array for printing.
@@ -1281,6 +1282,7 @@ def format_array(
         When formatting an Index subclass
         (e.g. IntervalIndex._format_native_types), we don't want the
         leading space since it should be left-aligned.
+    fallback_formatter
 
     Returns
     -------
@@ -1322,6 +1324,7 @@ def format_array(
         decimal=decimal,
         leading_space=leading_space,
         quoting=quoting,
+        fallback_formatter=fallback_formatter,
     )
 
     return fmt_obj.get_result()
@@ -1341,6 +1344,7 @@ def __init__(
         quoting: int | None = None,
         fixed_width: bool = True,
         leading_space: bool | None = True,
+        fallback_formatter: Callable | None = None,
     ) -> None:
         self.values = values
         self.digits = digits
@@ -1353,6 +1357,7 @@ def __init__(
         self.quoting = quoting
         self.fixed_width = fixed_width
         self.leading_space = leading_space
+        self.fallback_formatter = fallback_formatter
 
     def get_result(self) -> list[str]:
         fmt_values = self._format_strings()
@@ -1371,6 +1376,8 @@ def _format_strings(self) -> list[str]:
 
         if self.formatter is not None:
             formatter = self.formatter
+        elif self.fallback_formatter is not None:
+            formatter = self.fallback_formatter
         else:
             quote_strings = self.quoting is not None and self.quoting != QUOTE_NONE
             formatter = partial(
@@ -1419,7 +1426,7 @@ def _format(x):
 
         fmt_values = []
         for i, v in enumerate(vals):
-            if not is_float_type[i] and leading_space:
+            if not is_float_type[i] and leading_space or self.formatter is not None:
                 fmt_values.append(f" {_format(v)}")
             elif is_float_type[i]:
                 fmt_values.append(float_format(v))
@@ -1651,8 +1658,9 @@ def _format_strings(self) -> list[str]:
         values = extract_array(self.values, extract_numpy=True)
 
         formatter = self.formatter
+        fallback_formatter = None
         if formatter is None:
-            formatter = values._formatter(boxed=True)
+            fallback_formatter = values._formatter(boxed=True)
 
         if isinstance(values, Categorical):
             # Categorical is special for now, so that we can preserve tzinfo
@@ -1671,6 +1679,7 @@ def _format_strings(self) -> list[str]:
             decimal=self.decimal,
             leading_space=self.leading_space,
             quoting=self.quoting,
+            fallback_formatter=fallback_formatter,
         )
         return fmt_values
 

pandas/tests/frame/test_repr_info.py

@@ -365,3 +365,17 @@ def test_datetime64tz_slice_non_truncate(self):
         df = df.iloc[:, :5]
         result = repr(df)
         assert result == expected
+
+    def test_masked_ea_with_formatter(self):
+        # GH#39336
+        df = DataFrame(
+            {
+                "a": Series([0.123456789, 1.123456789], dtype="Float64"),
+                "b": Series([1, 2], dtype="Int64"),
+            }
+        )
+        result = df.to_string(formatters=["{:.2f}".format, "{:.2f}".format])
+        expected = """      a     b
+0  0.12  1.00
+1  1.12  2.00"""
+        assert result == expected