Merge pull request #8557 from jreback/dt_perf

PERF: fixup datetime_index repr perf (GH8556)

Author: jreback

pandas/core/format.py

@@ -2027,14 +2027,19 @@ def _format_datetime64_dateonly(x, nat_rep='NaT', date_format=None):
 
 
 def _is_dates_only(values):
-    for d in values:
-        if isinstance(d, np.datetime64):
-            d = Timestamp(d)
-
-        if d is not None and not lib.checknull(d) and d._has_time_component():
-            return False
-    return True
+    # return a boolean if we are only dates (and don't have a timezone)
+    from pandas import DatetimeIndex
+    values = DatetimeIndex(values)
+    if values.tz is not None:
+        return False
 
+    values_int = values.asi8
+    consider_values = values_int != iNaT
+    one_day_nanos = (86400 * 1e9)
+    even_days = np.logical_and(consider_values, values_int % one_day_nanos != 0).sum() == 0
+    if even_days:
+        return True
+    return False
 
 def _get_format_datetime64(is_dates_only, nat_rep='NaT', date_format=None):
 

vb_suite/index_object.py

@@ -108,7 +108,7 @@
 
 
 # Constructing MultiIndex from cartesian product of iterables
-# 
+#
 
 setup = common_setup + """
 iterables = [tm.makeStringIndex(10000), xrange(20)]
@@ -130,3 +130,14 @@
     Benchmark("MultiIndex.from_product([level1, level2]).values", setup,
               name='multiindex_with_datetime_level',
               start_date=datetime(2014, 10, 11))
+
+#----------------------------------------------------------------------
+# repr
+
+setup = common_setup + """
+dr = pd.date_range('20000101', freq='D', periods=100000)
+"""
+
+datetime_index_repr = \
+    Benchmark("dr._is_dates_only", setup,
+              start_date=datetime(2012, 1, 11))