ENH: Add min date function (pandas-dev#478)

* ENH: Add min date function

Add min date function to match max date function

* TST: Add test for min and max dates

Add test for min and max dates

* ENH: Improve error for min/max date

Raise NoDataFoundException rather than TypeError when no result
is returned.

arctic/tickstore/tickstore.py

@@ -754,4 +754,21 @@ def max_date(self, symbol):
         """
         res = self._collection.find_one({SYMBOL: symbol}, projection={ID: 0, END: 1},
                                         sort=[(START, pymongo.DESCENDING)])
+        if res is None:
+            raise NoDataFoundException("No Data found for {}".format(symbol))
         return utc_dt_to_local_dt(res[END])
+
+    def min_date(self, symbol):
+        """
+        Return the minimum datetime stored for a particular symbol
+
+        Parameters
+        ----------
+        symbol : `str`
+            symbol name for the item
+        """
+        res = self._collection.find_one({SYMBOL: symbol}, projection={ID: 0, START: 1},
+                                        sort=[(START, pymongo.ASCENDING)])
+        if res is None:
+            raise NoDataFoundException("No Data found for {}".format(symbol))
+        return utc_dt_to_local_dt(res[START])

tests/integration/tickstore/test_toplevel.py

@@ -216,3 +216,29 @@ def test_should_write_top_level_with_correct_timezone(arctic):
     lib2010 = arctic['FEED_2010.LEVEL1']
     # Check that only one point was written into 2010 being 3am on 31st
     assert len(lib2010.read('blah', DateRange(start=dt(2010, 12, 1), end=dt(2011, 1, 1)))) == 1
+
+
+def test_min_max_date(arctic):
+    arctic.initialize_library('FEED_2010.LEVEL1', tickstore.TICK_STORE_TYPE)
+    tstore = arctic['FEED_2010.LEVEL1']
+    dates = pd.date_range('20100101', periods=6, tz=mktz('Europe/London'))
+    df = pd.DataFrame(np.random.randn(6, 4), index=dates, columns=list('ABCD'))
+    tstore.write('blah', df)
+
+    min_date = tstore.min_date('blah')
+    max_date = tstore.max_date('blah')
+    assert min_date == dates[0].to_pydatetime()
+    assert max_date == dates[-1].to_pydatetime()
+
+
+def test_no_min_max_date(arctic):
+    arctic.initialize_library('FEED_2010.LEVEL1', tickstore.TICK_STORE_TYPE)
+    tstore = arctic['FEED_2010.LEVEL1']
+    dates = pd.date_range('20100101', periods=6, tz=mktz('Europe/London'))
+    df = pd.DataFrame(np.random.randn(6, 4), index=dates, columns=list('ABCD'))
+    tstore.write('blah', df)
+
+    with pytest.raises(NoDataFoundException):
+        tstore.min_date('unknown-symbol')
+    with pytest.raises(NoDataFoundException):
+        tstore.max_date('unknown-symbol')