PERF: improve perf of float-based timeseries plotting (#15073)

Author: jorisvandenbossche

asv_bench/benchmarks/plotting.py

@@ -20,6 +20,9 @@ def setup(self):
     def time_plot_regular(self):
         self.df.plot()
 
+    def time_plot_regular_compat(self):
+        self.df.plot(x_compat=True)
+
 
 class Misc(object):
     goal_time = 0.6

doc/source/whatsnew/v0.20.0.txt

@@ -281,10 +281,14 @@ Performance Improvements
 
 - Improved performance of ``pd.wide_to_long()`` (:issue:`14779`)
 - Increased performance of ``pd.factorize()`` by releasing the GIL with ``object`` dtype when inferred as strings (:issue:`14859`)
+- Improved performance of timeseries plotting with an irregular DatetimeIndex
+  (or with ``compat_x=True``) (:issue:`15073`).
+
 
 - When reading buffer object in ``read_sas()`` method without specified format, filepath string is inferred rather than buffer object.
 
 
+
 .. _whatsnew_0200.bug_fixes:
 
 Bug Fixes

pandas/tseries/converter.py

@@ -212,7 +212,7 @@ def try_parse(values):
             try:
                 values = tools.to_datetime(values)
                 if isinstance(values, Index):
-                    values = values.map(_dt_to_float_ordinal)
+                    values = _dt_to_float_ordinal(values)
                 else:
                     values = [_dt_to_float_ordinal(x) for x in values]
             except Exception:

pandas/tseries/tests/test_converter.py

@@ -3,7 +3,7 @@
 import nose
 
 import numpy as np
-from pandas import Timestamp, Period, Index
+from pandas import Timestamp, Period
 from pandas.compat import u
 import pandas.util.testing as tm
 from pandas.tseries.offsets import Second, Milli, Micro
@@ -104,8 +104,8 @@ def test_dateindex_conversion(self):
         for freq in ('B', 'L', 'S'):
             dateindex = tm.makeDateIndex(k=10, freq=freq)
             rs = self.dtc.convert(dateindex, None, None)
-            xp = Index(converter.dates.date2num(dateindex._mpl_repr()))
-            tm.assert_index_equal(rs, xp, decimals)
+            xp = converter.dates.date2num(dateindex._mpl_repr())
+            tm.assert_almost_equal(rs, xp, decimals)
 
     def test_resolution(self):
         def _assert_less(ts1, ts2):