BUG: do not assume 0 is in index of potential Series

Author: toobaz

doc/source/v0.15.0.txt

@@ -327,6 +327,7 @@ Bug Fixes
   date-likes incorrectly (:issue:`7762`, :issue:`7032`).
 
 
+- Bug in ``Series.str.cat`` with an index which was filtered as to not include the first item (:issue:`7857`)
 
 
 

pandas/core/strings.py

@@ -12,7 +12,8 @@
 
 
 def _get_array_list(arr, others):
-    if len(others) and isinstance(others[0], (list, np.ndarray)):
+    if len(others) and isinstance(_values_from_object(others)[0],
+                                  (list, np.ndarray, Series)):
         arrays = [arr] + list(others)
     else:
         arrays = [arr, others]

pandas/tests/test_strings.py

@@ -16,7 +16,7 @@
 from pandas.compat import range, lrange, u
 import pandas.compat as compat
 from pandas import (Index, Series, TimeSeries, DataFrame, isnull, notnull,
-                    bdate_range, date_range)
+                    bdate_range, date_range, MultiIndex)
 import pandas.core.common as com
 
 from pandas.util.testing import assert_series_equal, assert_almost_equal
@@ -1193,6 +1193,23 @@ def test_encode_decode_errors(self):
 
         tm.assert_series_equal(result, exp)
 
+    def test_cat_on_filtered_index(self):
+        df = DataFrame(index=MultiIndex.from_product([[2011, 2012], [1,2,3]],
+                                                     names=['year', 'month']))
+
+        df = df.reset_index()
+        df = df[df.month > 1]
+
+        str_year = df.year.astype('str')
+        str_month = df.month.astype('str')
+        str_both = str_year.str.cat(str_month, sep=' ')
+
+        self.assertEqual(str_both.loc[1], '2011 2')
+
+        str_multiple = str_year.str.cat([str_month, str_month], sep=' ')
+
+        self.assertEqual(str_multiple.loc[1], '2011 2 2')
+
 
 if __name__ == '__main__':
     nose.runmodule(argv=[__file__, '-vvs', '-x', '--pdb', '--pdb-failure'],