Merge branch 'StataParser' of https://github.com/PKEuS/pandas into PKEuS-StataParser

Conflicts:
	doc/source/release.rst

Author: jreback

doc/source/release.rst

@@ -290,6 +290,7 @@ Bug Fixes
 - Bug in ``pd.read_stata`` which would use the wrong data types and missing values (:issue:`6327`)
 - Bug in ``DataFrame.to_stata`` that lead to data loss in certain cases, and could exported using the
   wrong data types and missing values (:issue:`6335`)
+- StataWriter replaces missing values in string columns by empty string (:issue:`6802`)
 - Inconsistent types in Timestamp addition/subtraction (:issue:`6543`)
 - Bug in preserving frequency across Timestamp addition/subtraction (:issue:`4547`)
 - Bug in indexing: empty list lookup caused ``IndexError`` exceptions (:issue:`6536`, :issue:`6551`)
@@ -314,6 +315,7 @@ Bug Fixes
   as regexs even when ``regex=False`` (:issue:`6777`).
 - Bug in timedelta ops on 32-bit platforms (:issue:`6808`)
 - Bug in setting a tz-aware index directly via ``.index`` (:issue:`6785`)
+<<<<<<< HEAD
 - Bug in expressions.py where numexpr would try to evaluate arithmetic ops
   (:issue:`6762`).
 - Bug in Makefile where it didn't remove Cython generated C files with ``make

pandas/io/stata.py

@@ -1319,6 +1319,8 @@ def _write_data_nodates(self):
             for i, var in enumerate(row):
                 typ = ord(typlist[i])
                 if typ <= 244:  # we've got a string
+                    if var is None or var == np.nan:
+                        var = _pad_bytes('', typ)
                     if len(var) < typ:
                         var = _pad_bytes(var, typ)
                     self._write(var)

pandas/io/tests/test_stata.py

@@ -508,6 +508,16 @@ def test_date_export_formats(self):
             tm.assert_frame_equal(written_and_read_again.set_index('index'),
                                   expected)
 
+    def test_write_missing_strings(self):
+        original = DataFrame([["1"], [None]], columns=["foo"])
+        expected = DataFrame([["1"], [""]], columns=["foo"])
+        expected.index.name = 'index'
+        with tm.ensure_clean() as path:
+            original.to_stata(path)
+            written_and_read_again = self.read_dta(path)
+            tm.assert_frame_equal(written_and_read_again.set_index('index'),
+                                  expected)
+
 
 if __name__ == '__main__':
     nose.runmodule(argv=[__file__, '-vvs', '-x', '--pdb', '--pdb-failure'],