BUG: pd.NA being cast to NaN during output formatting (#55754)

Author: dominiquegarmier

pandas/io/formats/format.py

@@ -696,9 +696,9 @@ def _truncate_vertically(self) -> None:
         assert self.max_rows_fitted is not None
         row_num = self.max_rows_fitted // 2
         if row_num >= 1:
-            head = self.tr_frame.iloc[:row_num, :]
-            tail = self.tr_frame.iloc[-row_num:, :]
-            self.tr_frame = concat((head, tail))
+            _len = len(self.tr_frame)
+            _slice = np.hstack([np.arange(row_num), np.arange(_len - row_num, _len)])
+            self.tr_frame = self.tr_frame.iloc[_slice]
         else:
             row_num = cast(int, self.max_rows)
             self.tr_frame = self.tr_frame.iloc[:row_num, :]

pandas/tests/io/formats/test_format.py

@@ -171,6 +171,12 @@ def test_repr_truncation(self):
         with option_context("display.max_colwidth", max_len + 2):
             assert "..." not in repr(df)
 
+    def test_repr_truncation_preserves_na(self):
+        # https://github.com/pandas-dev/pandas/issues/55630
+        df = DataFrame({"a": [pd.NA for _ in range(10)]})
+        with option_context("display.max_rows", 2, "display.show_dimensions", False):
+            assert repr(df) == "       a\n0   <NA>\n..   ...\n9   <NA>"
+
     def test_max_colwidth_negative_int_raises(self):
         # Deprecation enforced from:
         # https://github.com/pandas-dev/pandas/issues/31532