ENH: Add a reader base which reindexes results.

Working towards history results which contain mixed asset types, add
a reader which makes `load_raw_arrays` return results indexed on the
session/minute ranges specified by the specified `trading_calendar`
instead of the calendar of the backing reader.

This reader will be used to make Equity readers align with Future
readers. It is intended for use as part of another reader (which will
dispatch queries based on asset type and then recombined results) which
will be passed to the `[Minute|Session]HistoryLoaders in the data portal.

tests/data/test_resample.py

@@ -16,7 +16,7 @@ from numbers import Real
 
 from nose_parameterized import parameterized
 from numpy.testing import assert_almost_equal
-from numpy import nan, array
+from numpy import nan, array, full
 import pandas as pd
 from pandas import DataFrame
 from six import iteritems
@@ -25,11 +25,14 @@ from zipline.data.resample import (
     minute_to_session,
     DailyHistoryAggregator,
     MinuteResampleSessionBarReader,
+    ReindexMinuteBarReader,
+    ReindexSessionBarReader,
 )
 
 from zipline.testing.fixtures import (
     WithEquityMinuteBarData,
     WithBcolzEquityMinuteBarReader,
+    WithBcolzEquityDailyBarReader,
     WithBcolzFutureMinuteBarReader,
     ZiplineTestCase,
 )
@@ -527,3 +530,124 @@ class TestResampleSessionBars(WithBcolzFutureMinuteBarReader,
                     assert_almost_equal(values[col], result,
                                         err_msg="sid={0} col={1} dt={2}".
                                         format(sid, col, dt))
+
+
+class TestReindexMinuteBars(WithBcolzEquityMinuteBarReader,
+                            ZiplineTestCase):
+
+    TRADING_CALENDAR_STRS = ('CME', 'NYSE')
+    TRADING_CALENDAR_PRIMARY_CAL = 'CME'
+
+    ASSET_FINDER_EQUITY_SIDS = 1, 2, 3
+
+    START_DATE = pd.Timestamp('2015-12-01', tz='UTC')
+    END_DATE = pd.Timestamp('2015-12-31', tz='UTC')
+
+    def test_load_raw_arrays(self):
+        reindex_reader = ReindexMinuteBarReader(
+            self.trading_calendar,
+            self.bcolz_equity_minute_bar_reader,
+            self.START_DATE,
+            self.END_DATE,
+        )
+        m_open, m_close = self.trading_calendar.open_and_close_for_session(
+            self.START_DATE)
+        outer_minutes = self.trading_calendar.minutes_in_range(m_open, m_close)
+        result = reindex_reader.load_raw_arrays(
+            OHLCV, m_open, m_close, [1, 2])
+
+        opens = DataFrame(data=result[0], index=outer_minutes,
+                          columns=[1, 2])
+        opens_with_price = opens.dropna()
+
+        self.assertEqual(
+            1440,
+            len(opens),
+            "The result should have 1440 bars, the number of minutes in a "
+            "trading session on the target calendar."
+        )
+
+        self.assertEqual(
+            390,
+            len(opens_with_price),
+            "The result, after dropping nans, should have 390 bars, the "
+            " number of bars in a trading session in the reader's calendar."
+        )
+
+        slicer = outer_minutes.slice_indexer(
+            end=pd.Timestamp('2015-12-01 14:30', tz='UTC'))
+
+        assert_almost_equal(
+            opens[1][slicer],
+            full(slicer.stop, nan),
+            err_msg="All values before the NYSE market open should be nan.")
+
+        slicer = outer_minutes.slice_indexer(
+            start=pd.Timestamp('2015-12-01 21:01', tz='UTC'))
+
+        assert_almost_equal(
+            opens[1][slicer],
+            full(slicer.stop - slicer.start, nan),
+            err_msg="All values after the NYSE market close should be nan.")
+
+        first_minute_loc = outer_minutes.get_loc(pd.Timestamp(
+            '2015-12-01 14:31', tz='UTC'))
+
+        # Spot check a value.
+        # The value is the autogenerated value from test fixtures.
+        assert_almost_equal(
+            10.0,
+            opens[1][first_minute_loc],
+            err_msg="The value for Equity 1, should be 10.0, at NYSE open.")
+
+
+class TestReindexSessionBars(WithBcolzEquityDailyBarReader,
+                             ZiplineTestCase):
+
+    TRADING_CALENDAR_STRS = ('CME', 'NYSE')
+    TRADING_CALENDAR_PRIMARY_CAL = 'CME'
+
+    ASSET_FINDER_EQUITY_SIDS = 1, 2, 3
+
+    # Dates are chosen to span Thanksgiving, which is not a Holiday on CME.
+    START_DATE = pd.Timestamp('2015-11-01', tz='UTC')
+    END_DATE = pd.Timestamp('2015-11-30', tz='UTC')
+
+    def test_load_raw_arrays(self):
+        reindex_reader = ReindexSessionBarReader(
+            self.trading_calendar,
+            self.bcolz_equity_daily_bar_reader,
+            self.START_DATE,
+            self.END_DATE,
+        )
+
+        outer_sessions = self.trading_calendar.sessions_in_range(
+            self.START_DATE, self.END_DATE)
+
+        result = reindex_reader.load_raw_arrays(
+            OHLCV, self.START_DATE, self.END_DATE, [1, 2])
+
+        opens = DataFrame(data=result[0], index=outer_sessions,
+                          columns=[1, 2])
+        opens_with_price = opens.dropna()
+
+        self.assertEqual(
+            21,
+            len(opens),
+            "The reindexed result should have 21 days, which is the number of "
+            "business days in 2015-11")
+        self.assertEqual(
+            20,
+            len(opens_with_price),
+            "The reindexed result after dropping nans should have 20 days, "
+            "because Thanksgiving is a NYSE holiday.")
+
+        # Thanksgiving, 2015-11-26.
+        # Is a holiday in NYSE, but not in CME.
+        tday_loc = outer_sessions.get_loc(pd.Timestamp('2015-11-26', tz='UTC'))
+
+        assert_almost_equal(
+            nan,
+            opens[1][tday_loc],
+            err_msg="2015-11-26 should be `nan`, since Thanksgiving is a "
+            "holiday in the reader's calendar.")