Merge pull request #5733 from nmichaud/read_table_prefix_fix

Fix prefix argument for read_csv/read_table

Author: y-p

pandas/io/parsers.py

@@ -980,7 +980,7 @@ def __init__(self, src, **kwds):
 
         if self.names is None:
             if self.prefix:
-                self.names = ['X%d' % i
+                self.names = ['%s%d' % (self.prefix, i)
                               for i in range(self._reader.table_width)]
             else:
                 self.names = lrange(self._reader.table_width)
@@ -1571,7 +1571,7 @@ def _infer_columns(self):
             num_original_columns = ncols
             if not names:
                 if self.prefix:
-                    columns = [['X%d' % i for i in range(ncols)]]
+                    columns = [['%s%d' % (self.prefix,i) for i in range(ncols)]]
                 else:
                     columns = [lrange(ncols)]
                 columns = self._handle_usecols(columns, columns[0])

pandas/io/tests/test_parsers.py

@@ -968,6 +968,22 @@ def test_no_header(self):
 
         self.assert_(np.array_equal(df2.columns, names))
 
+    def test_no_header_prefix(self):
+        data = """1,2,3,4,5
+6,7,8,9,10
+11,12,13,14,15
+"""
+        df_pref = self.read_table(StringIO(data), sep=',', prefix='Field',
+                                  header=None)
+
+        expected = [[1, 2, 3, 4, 5.],
+                    [6, 7, 8, 9, 10],
+                    [11, 12, 13, 14, 15]]
+        tm.assert_almost_equal(df_pref.values, expected)
+
+        self.assert_(np.array_equal(df_pref.columns,
+                                    ['Field0', 'Field1', 'Field2', 'Field3', 'Field4']))
+
     def test_header_with_index_col(self):
         data = """foo,1,2,3
 bar,4,5,6