Merge pull request pandas-dev#10023 from jblackburne/read_csv-newline-chunk

read_csv newline fix

Author: jreback

doc/source/whatsnew/v0.16.1.txt

@@ -298,6 +298,7 @@ Bug Fixes
 - Bug ``GroupBy.size`` doesn't attach index name properly if grouped by ``TimeGrouper`` (:issue:`9925`)
 - Bug causing an exception in slice assignments because ``length_of_indexer`` returns wrong results (:issue:`9995`)
 - Bug in csv parser causing lines with initial whitespace plus one non-space character to be skipped. (:issue:`9710`)
+- Bug in C csv parser causing spurious NaNs when data started with newline followed by whitespace. (:issue:`10022`)
 
 - Bug causing elements with a null group to spill into the final group when grouping by a ``Categorical`` (:issue:`9603`)
 - Bug where .iloc and .loc behavior is not consistent on empty dataframes (:issue:`9964`)

pandas/io/tests/test_parsers.py

@@ -2287,6 +2287,12 @@ def test_single_char_leading_whitespace(self):
         result = self.read_csv(StringIO(data), skipinitialspace=True)
         tm.assert_frame_equal(result, expected)
 
+    def test_chunk_begins_with_newline_whitespace(self):
+        # GH 10022
+        data = '\n hello\nworld\n'
+        result = self.read_csv(StringIO(data), header=None)
+        self.assertEqual(len(result), 2)
+
 
 class TestPythonParser(ParserTests, tm.TestCase):
     def test_negative_skipfooter_raises(self):

pandas/src/parser/tokenizer.c

@@ -854,7 +854,7 @@ int tokenize_delimited(parser_t *self, size_t line_limit)
                     --i;
                 } while (i + 1 > self->datapos && *buf != '\n');
 
-                if (i + 1 > self->datapos) // reached a newline rather than the beginning
+                if (*buf == '\n') // reached a newline rather than the beginning
                 {
                     ++buf; // move pointer to first char after newline
                     ++i;
@@ -1172,7 +1172,7 @@ int tokenize_delim_customterm(parser_t *self, size_t line_limit)
                     --i;
                 } while (i + 1 > self->datapos && *buf != self->lineterminator);
 
-                if (i + 1 > self->datapos) // reached a newline rather than the beginning
+                if (*buf == self->lineterminator) // reached a newline rather than the beginning
                 {
                     ++buf; // move pointer to first char after newline
                     ++i;