ENH: PeriodIndex can accept freq with mult

Author: sinhrks

doc/source/timeseries.rst

@@ -1152,6 +1152,12 @@ The ``PeriodIndex`` constructor can also be used directly:
 
    PeriodIndex(['2011-1', '2011-2', '2011-3'], freq='M')
 
+Passing multiplied freq results in specified interval with normal freq:
+
+.. ipython:: python
+
+   PeriodIndex(start='2014-01', freq='3M', periods=4)
+
 Just like ``DatetimeIndex``, a ``PeriodIndex`` can also be used to index pandas
 objects:
 

doc/source/whatsnew/v0.15.2.txt

@@ -67,6 +67,8 @@ Enhancements
 - Added Google Analytics (`pandas.io.ga`) basic documentation (:issue:`8835`). See :ref:`here<remote_data.ga>`.
 - Added flag ``order_categoricals`` to ``StataReader`` and ``read_stata`` to select whether to order imported categorical data (:issue:`8836`).  See :ref:`here <io.stata-categorical>` for more information on importing categorical variables from Stata data files.
 
+- ``PeriodIndex`` and ``period_range`` can now accept multiplied freq (:issue:`7811`)
+
 .. _whatsnew_0152.performance:
 
 Performance

pandas/tseries/period.py

@@ -1275,10 +1275,14 @@ def tz_localize(self, tz, infer_dst=False):
 PeriodIndex._add_datetimelike_methods()
 
 
-def _get_ordinal_range(start, end, periods, freq):
+def _get_ordinal_range(start, end, periods, freq, mult=1):
     if com._count_not_none(start, end, periods) < 2:
         raise ValueError('Must specify 2 of start, end, periods')
 
+    if freq is not None:
+        _, mult = _gfc(freq)
+        freq = frequencies.get_base_alias(freq)
+
     if start is not None:
         start = Period(start, freq)
     if end is not None:
@@ -1302,15 +1306,15 @@ def _get_ordinal_range(start, end, periods, freq):
             raise ValueError('Could not infer freq from start/end')
 
     if periods is not None:
+        periods = periods * mult
         if start is None:
-            data = np.arange(end.ordinal - periods + 1,
-                             end.ordinal + 1,
+            data = np.arange(end.ordinal - periods + mult, end.ordinal + 1, mult,
                              dtype=np.int64)
         else:
-            data = np.arange(start.ordinal, start.ordinal + periods,
+            data = np.arange(start.ordinal, start.ordinal + periods, mult,
                              dtype=np.int64)
     else:
-        data = np.arange(start.ordinal, end.ordinal + 1, dtype=np.int64)
+        data = np.arange(start.ordinal, end.ordinal + 1, mult, dtype=np.int64)
 
     return data, freq
 
@@ -1348,7 +1352,6 @@ def _range_from_fields(year=None, month=None, quarter=None, day=None,
         base, mult = _gfc(freq)
         if mult != 1:
             raise ValueError('Only mult == 1 supported')
-
         arrays = _make_field_arrays(year, month, day, hour, minute, second)
         for y, mth, d, h, mn, s in zip(*arrays):
             ordinals.append(tslib.period_ordinal(y, mth, d, h, mn, s, 0, 0, base))

pandas/tseries/tests/test_period.py

@@ -1291,6 +1291,42 @@ def test_constructor_year_and_quarter(self):
         p = PeriodIndex(lops)
         tm.assert_index_equal(p, idx)
 
+    def test_constructor_freq_mult(self):
+        # GH #7811
+        for func in [PeriodIndex, period_range]:
+            # must be the same, but for sure...
+            pidx = func(start='2014-01', freq='2M', periods=4)
+            expected = PeriodIndex(['2014-01', '2014-03', '2014-05', '2014-07'], freq='M')
+            tm.assert_index_equal(pidx, expected)
+
+            pidx = func(start='2014-01-02', end='2014-01-15', freq='3D')
+            expected = PeriodIndex(['2014-01-02', '2014-01-05', '2014-01-08', '2014-01-11',
+                                    '2014-01-14'], freq='D')
+            tm.assert_index_equal(pidx, expected)
+
+            pidx = func(end='2014-01-01 17:00', freq='4H', periods=3)
+            expected = PeriodIndex(['2014-01-01 09:00', '2014-01-01 13:00',
+                                    '2014-01-01 17:00'], freq='H')
+            tm.assert_index_equal(pidx, expected)
+
+    def test_constructor_freq_mult_dti_compat(self):
+        import itertools
+        mults = [1, 2, 3, 4, 5] # -1, -2, -3, -4, -5]
+        freqs = ['A', 'M', 'D', 'T', 'S']
+        for mult, freq in itertools.product(mults, freqs):
+            freqstr = str(mult) + freq
+            pidx = PeriodIndex(start='2014-04-01', freq=freqstr, periods=10)
+            expected = date_range(start='2014-04-01', freq=freqstr, periods=10).to_period(freq)
+            tm.assert_index_equal(pidx, expected)
+
+        mults = [-1, -2, -3, -4, -5]
+        freqs = ['D', 'T', 'S']
+        for mult, freq in itertools.product(mults, freqs):
+            freqstr = str(mult) + freq
+            pidx = PeriodIndex(start='2014-04-01', freq=freqstr, periods=10)
+            expected = date_range(start='2014-04-01', freq=freqstr, periods=10).to_period(freq)
+            tm.assert_index_equal(pidx, expected)
+
     def test_is_(self):
         create_index = lambda: PeriodIndex(freq='A', start='1/1/2001',
                                            end='12/1/2009')
@@ -2149,34 +2185,28 @@ def test_to_period_monthish(self):
             self.assertEqual(prng.freq, 'M')
 
     def test_no_multiples(self):
-        self.assertRaises(ValueError, period_range, '1989Q3', periods=10,
-                          freq='2Q')
-
-        self.assertRaises(ValueError, period_range, '1989', periods=10,
-                          freq='2A')
         self.assertRaises(ValueError, Period, '1989', freq='2A')
 
-    # def test_pindex_multiples(self):
-    #     pi = PeriodIndex(start='1/1/10', end='12/31/12', freq='2M')
-    #     self.assertEqual(pi[0], Period('1/1/10', '2M'))
-    #     self.assertEqual(pi[1], Period('3/1/10', '2M'))
-
-    #     self.assertEqual(pi[0].asfreq('6M'), pi[2].asfreq('6M'))
-    #     self.assertEqual(pi[0].asfreq('A'), pi[2].asfreq('A'))
-
-    #     self.assertEqual(pi[0].asfreq('M', how='S'),
-    #                       Period('Jan 2010', '1M'))
-    #     self.assertEqual(pi[0].asfreq('M', how='E'),
-    #                       Period('Feb 2010', '1M'))
-    #     self.assertEqual(pi[1].asfreq('M', how='S'),
-    #                       Period('Mar 2010', '1M'))
-
-    #     i = Period('1/1/2010 12:05:18', '5S')
-    #     self.assertEqual(i, Period('1/1/2010 12:05:15', '5S'))
-
-    #     i = Period('1/1/2010 12:05:18', '5S')
-    #     self.assertEqual(i.asfreq('1S', how='E'),
-    #                       Period('1/1/2010 12:05:19', '1S'))
+    def test_pindex_multiples(self):
+        pi = PeriodIndex(start='1/1/11', end='12/31/11', freq='2M')
+        expected = PeriodIndex(['2011-01', '2011-03', '2011-05', '2011-07',
+                                '2011-09', '2011-11'], freq='M')
+        tm.assert_index_equal(pi, expected)
+        self.assertEqual(pi.freq, 'M')
+
+        pi = period_range(start='1/1/11', end='12/31/11', freq='2M')
+        tm.assert_index_equal(pi, expected)
+        self.assertEqual(pi.freq, 'M')
+
+        pi = period_range(start='1/1/11', periods=6, freq='2M')
+        tm.assert_index_equal(pi, expected)
+        self.assertEqual(pi.freq, 'M')
+
+        pi = period_range(start='2011-11-30', periods=6, freq='-2M')
+        expected = PeriodIndex(['2011-11', '2011-09', '2011-07', '2011-05',
+                                '2011-03', '2011-01'], freq='M')
+        tm.assert_index_equal(pi, expected)
+        self.assertEqual(pi.freq, 'M')
 
     def test_iteration(self):
         index = PeriodIndex(start='1/1/10', periods=4, freq='B')