Merge pull request #6486 from jreback/reindex

PERF: perf improvements in single-dtyped indexing (GH6484)

Author: jreback

doc/source/release.rst

@@ -129,6 +129,7 @@ Improvements to existing features
   using ``DataFrame.to_csv`` (:issue:`5414`, :issue:`4528`)
 - perf improvements in DataFrame construction with certain offsets, by removing faulty caching
   (e.g. MonthEnd,BusinessMonthEnd), (:issue:`6479`)
+- perf improvements in single-dtyped indexing (:issue:`6484`)
 
 .. _release.bug_fixes-0.14.0:
 

pandas/core/internals.py

@@ -3402,8 +3402,11 @@ def reindex_items(self, new_items, indexer=None, copy=True,
             # unique
             if self.axes[0].is_unique and new_items.is_unique:
 
+                # ok to use the global indexer if only 1 block
+                i = indexer if len(self.blocks) == 1 else None
+
                 for block in self.blocks:
-                    blk = block.reindex_items_from(new_items, copy=copy)
+                    blk = block.reindex_items_from(new_items, indexer=i, copy=copy)
                     new_blocks.extend(_valid_blocks(blk))
 
             # non-unique