special casing in freq_infer

Author: jbrockmendel

pandas/core/arrays/timedeltas.py

@@ -7,7 +7,7 @@
 
 import numpy as np
 
-from pandas._libs import algos, tslibs
+from pandas._libs import tslibs
 from pandas._libs.tslibs import NaT, Timedelta, Timestamp, iNaT
 from pandas._libs.tslibs.fields import get_timedelta_field
 from pandas._libs.tslibs.timedeltas import (
@@ -24,7 +24,7 @@
 from pandas.core.dtypes.missing import isna
 
 from pandas.core import ops
-from pandas.core.algorithms import checked_add_with_arr, unique1d
+from pandas.core.algorithms import checked_add_with_arr
 import pandas.core.common as com
 
 from pandas.tseries.frequencies import to_offset
@@ -241,22 +241,6 @@ def _validate_fill_value(self, fill_value):
                              "Got '{got}'.".format(got=fill_value))
         return fill_value
 
-    # is_monotonic_increasing, is_monotonic_decreasing, and is_unique
-    #  are needed by `frequencies.infer_freq`, which is called when accessing
-    #  the `inferred_freq` property inside the TimedeltaArray constructor
-
-    @property  # NB: override with cache_readonly in immutable subclasses
-    def is_monotonic_increasing(self):
-        return algos.is_monotonic(self.asi8, timelike=True)[0]
-
-    @property  # NB: override with cache_readonly in immutable subclasses
-    def is_monotonic_decreasing(self):
-        return algos.is_monotonic(self.asi8, timelike=True)[1]
-
-    @property  # NB: override with cache_readonly in immutable subclasses
-    def is_unique(self):
-        return len(unique1d(self.asi8)) == len(self)
-
     # ----------------------------------------------------------------
     # Arithmetic Methods
 

pandas/tseries/frequencies.py

@@ -5,7 +5,7 @@
 import numpy as np
 from pytz import AmbiguousTimeError
 
-from pandas._libs.algos import unique_deltas
+from pandas._libs.algos import is_monotonic, unique_deltas
 from pandas._libs.tslibs import Timedelta, Timestamp
 from pandas._libs.tslibs.ccalendar import MONTH_ALIASES, int_to_weekday
 from pandas._libs.tslibs.conversion import tz_convert
@@ -295,8 +295,19 @@ def __init__(self, index, warn=True):
         if len(index) < 3:
             raise ValueError('Need at least 3 dates to infer frequency')
 
-        self.is_monotonic = (self.index.is_monotonic_increasing or
-                             self.index.is_monotonic_decreasing)
+        if not hasattr(index, "is_monotonic_increasing"):
+            # i.e. TimedeltaArray, not TimedeltaIndex
+            increasing, decreasing, strict = is_monotonic(index.asi8,
+                                                          timelike=True)
+            self.is_monotonic = increasing or decreasing
+            self.strictly_monotonic = strict
+        else:
+            self.is_monotonic = (index.is_monotonic_increasing or
+                                 index.is_monotonic_decreasing)
+            strict = False
+            if self.is_monotonic and index.is_unique:
+                strict = True
+            self.strictly_monotonic = strict
 
     @cache_readonly
     def deltas(self):
@@ -323,7 +334,7 @@ def get_freq(self):  # noqa:F811
         -------
         freqstr : str or None
         """
-        if not self.is_monotonic or not self.index.is_unique:
+        if not self.strictly_monotonic:
             return None
 
         delta = self.deltas[0]