ENH: GH11128 add weekday_name to DatetimeIndex and .dt

	Completed merge of Bahrunnur's PR 'weekday-name'
	Moved 'enhancements' to v0.18.1.txt
	Added tests to pandas/tests/series/test_datetime_values.py
	Added weekday_name property producing 'NaT' to NaTType class
 Author:    BastiaanBergman <Bastiaan.Bergman@gmailcom>

Author: bahrunnur

doc/source/api.rst

@@ -469,6 +469,7 @@ These can be accessed like ``Series.dt.<property>``.
    Series.dt.days_in_month
    Series.dt.tz
    Series.dt.freq
+   Series.dt.weekday_name
 
 **Datetime Methods**
 
@@ -1487,6 +1488,7 @@ Time/Date Components
    DatetimeIndex.is_year_start
    DatetimeIndex.is_year_end
    DatetimeIndex.inferred_freq
+   DatetimeIndex.weekday_name
 
 Selecting
 ~~~~~~~~~

doc/source/timeseries.rst

@@ -523,6 +523,7 @@ There are several time/date properties that one can access from ``Timestamp`` or
     is_quarter_end,"Logical indicating if last day of quarter (defined by frequency)"
     is_year_start,"Logical indicating if first day of year (defined by frequency)"
     is_year_end,"Logical indicating if last day of year (defined by frequency)"
+    weekday_name,"The name of day in a week (ex: Friday)"
 
 Furthermore, if you have a ``Series`` with datetimelike values, then you can access these properties via the ``.dt`` accessor, see the :ref:`docs <basics.dt_accessors>`
 

doc/source/whatsnew/v0.18.1.txt

@@ -59,6 +59,7 @@ Other Enhancements
 - ``pd.read_csv()`` now supports opening files using xz compression, via extension inference or explicit ``compression='xz'`` is specified; ``xz`` compressions is also supported by ``DataFrame.to_csv`` in the same way (:issue:`11852`)
 - ``pd.read_msgpack()`` now always gives writeable ndarrays even when compression is used (:issue:`12359`).
 - ``Index.take`` now handles ``allow_fill`` and ``fill_value`` consistently (:issue:`12631`)
+- Added ``weekday_name`` as a component to ``DatetimeIndex`` and ``.dt`` accessor. (:issue:`11128`)
 
 .. ipython:: python
 

pandas/tests/series/test_datetime_values.py

@@ -37,7 +37,8 @@ def test_dt_namespace_accessor(self):
         ok_for_dt = ok_for_base + ['date', 'time', 'microsecond', 'nanosecond',
                                    'is_month_start', 'is_month_end',
                                    'is_quarter_start', 'is_quarter_end',
-                                   'is_year_start', 'is_year_end', 'tz']
+                                   'is_year_start', 'is_year_end', 'tz',
+                                   'weekday_name']
         ok_for_dt_methods = ['to_period', 'to_pydatetime', 'tz_localize',
                              'tz_convert', 'normalize', 'strftime', 'round',
                              'floor', 'ceil']

pandas/tseries/index.py

@@ -61,6 +61,9 @@ def f(self):
 
             result = tslib.get_start_end_field(
                 values, field, self.freqstr, month_kw)
+        elif field in ['weekday_name']:
+            result = tslib.get_date_name_field(values, field)
+            return self._maybe_mask_results(result)
         else:
             result = tslib.get_date_field(values, field)
 
@@ -208,7 +211,7 @@ def _join_i8_wrapper(joinf, **kwargs):
                          'daysinmonth', 'date', 'time', 'microsecond',
                          'nanosecond', 'is_month_start', 'is_month_end',
                          'is_quarter_start', 'is_quarter_end', 'is_year_start',
-                         'is_year_end', 'tz', 'freq']
+                         'is_year_end', 'tz', 'freq', 'weekday_name']
     _is_numeric_dtype = False
     _infer_as_myclass = True
 
@@ -1564,6 +1567,12 @@ def _set_freq(self, value):
         'dow',
         "The day of the week with Monday=0, Sunday=6")
     weekday = dayofweek
+
+    weekday_name = _field_accessor(
+        'weekday_name',
+        'weekday_name',
+        "The name of day in a week (ex: Friday)\n\n.. versionadded:: 0.18.1")
+
     dayofyear = _field_accessor(
         'dayofyear',
         'doy',

pandas/tseries/tests/test_base.py

@@ -32,7 +32,7 @@ def test_ops_properties(self):
                                    'is_month_start', 'is_month_end',
                                    'is_quarter_start',
                                    'is_quarter_end', 'is_year_start',
-                                   'is_year_end'],
+                                   'is_year_end', 'weekday_name'],
                                   lambda x: isinstance(x, DatetimeIndex))
 
     def test_ops_properties_basic(self):

pandas/tseries/tests/test_timeseries.py

@@ -959,7 +959,7 @@ def test_nat_vector_field_access(self):
     def test_nat_scalar_field_access(self):
         fields = ['year', 'quarter', 'month', 'day', 'hour', 'minute',
                   'second', 'microsecond', 'nanosecond', 'week', 'dayofyear',
-                  'days_in_month', 'daysinmonth', 'dayofweek']
+                  'days_in_month', 'daysinmonth', 'dayofweek', 'weekday_name']
         for field in fields:
             result = getattr(NaT, field)
             self.assertTrue(np.isnan(result))
@@ -1852,7 +1852,7 @@ def test_timestamp_fields(self):
         fields = ['dayofweek', 'dayofyear', 'week', 'weekofyear', 'quarter',
                   'days_in_month', 'is_month_start', 'is_month_end',
                   'is_quarter_start', 'is_quarter_end', 'is_year_start',
-                  'is_year_end']
+                  'is_year_end', 'weekday_name']
         for f in fields:
             expected = getattr(idx, f)[-1]
             result = getattr(Timestamp(idx[-1]), f)
@@ -3541,6 +3541,15 @@ def test_datetimeindex_accessors(self):
         self.assertEqual(dti.is_year_end[0], False)
         self.assertEqual(dti.is_year_end[364], True)
 
+        # GH 11128
+        self.assertEqual(dti.weekday_name[4], u'Monday')
+        self.assertEqual(dti.weekday_name[5], u'Tuesday')
+        self.assertEqual(dti.weekday_name[6], u'Wednesday')
+        self.assertEqual(dti.weekday_name[7], u'Thursday')
+        self.assertEqual(dti.weekday_name[8], u'Friday')
+        self.assertEqual(dti.weekday_name[9], u'Saturday')
+        self.assertEqual(dti.weekday_name[10], u'Sunday')
+
         self.assertEqual(len(dti.year), 365)
         self.assertEqual(len(dti.month), 365)
         self.assertEqual(len(dti.day), 365)
@@ -3558,6 +3567,7 @@ def test_datetimeindex_accessors(self):
         self.assertEqual(len(dti.is_quarter_end), 365)
         self.assertEqual(len(dti.is_year_start), 365)
         self.assertEqual(len(dti.is_year_end), 365)
+        self.assertEqual(len(dti.weekday_name), 365)
 
         dti = DatetimeIndex(freq='BQ-FEB', start=datetime(1998, 1, 1),
                             periods=4)

pandas/tslib.pyx

@@ -398,6 +398,11 @@ class Timestamp(_Timestamp):
     def dayofweek(self):
         return self.weekday()
 
+    @property
+    def weekday_name(self):
+        out = get_date_name_field(np.array([self.value], dtype=np.int64), 'weekday_name')
+        return out[0]
+
     @property
     def dayofyear(self):
         return self._get_field('doy')
@@ -667,7 +672,7 @@ class NaTType(_NaT):
 
 fields = ['year', 'quarter', 'month', 'day', 'hour',
           'minute', 'second', 'millisecond', 'microsecond', 'nanosecond',
-          'week', 'dayofyear', 'days_in_month', 'daysinmonth', 'dayofweek']
+          'week', 'dayofyear', 'days_in_month', 'daysinmonth', 'dayofweek', 'weekday_name']
 for field in fields:
     prop = property(fget=lambda self: np.nan)
     setattr(NaTType, field, prop)
@@ -4390,6 +4395,38 @@ def get_start_end_field(ndarray[int64_t] dtindex, object field, object freqstr=N
 
     raise ValueError("Field %s not supported" % field)
 
+@cython.wraparound(False)
+@cython.boundscheck(False)
+def get_date_name_field(ndarray[int64_t] dtindex, object field):
+    '''
+    Given a int64-based datetime index, return array of strings of date
+    name based on requested field (e.g. weekday_name)
+    '''
+    cdef:
+        _TSObject ts
+        Py_ssize_t i, count = 0
+        ndarray[object] out
+        pandas_datetimestruct dts
+        int dow
+
+    _dayname = np.array(
+        ['Monday', 'Tuesday', 'Wednesday', 'Thursday', 'Friday', 'Saturday', 'Sunday'],
+         dtype=np.str )
+
+    count = len(dtindex)
+    out = np.empty(count, dtype=object)
+
+    if field == 'weekday_name':
+        for i in range(count):
+            if dtindex[i] == NPY_NAT: out[i] = np.nan; continue
+
+            pandas_datetime_to_datetimestruct(dtindex[i], PANDAS_FR_ns, &dts)
+            dow = dayofweek(dts.year, dts.month, dts.day)
+            out[i] = _dayname[dow]
+        return out
+
+    raise ValueError("Field %s not supported" % field)
+
 
 cdef inline int m8_weekday(int64_t val):
     ts = convert_to_tsobject(val, None, None)