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ENH: Improve performance for df.__setitem__ with list-like indexers #38148

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Nov 29, 2020
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ENH: Improve performance for df.__setitem__ with list-like indexers #38148

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f953ff4
Fix performance problems for df.__setitem__ with lislike indexers
phofl Nov 29, 2020
322feb5
Improve code
phofl Nov 29, 2020
07b1c52
Adress review comments
phofl Nov 29, 2020
d4b76e5
Merge branch 'master' into 37954
jreback Nov 29, 2020
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4 changes: 4 additions & 0 deletions asv_bench/benchmarks/indexing.py
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Expand Up @@ -358,6 +358,10 @@ def time_assign_with_setitem(self):
for i in range(100):
self.df[i] = np.random.randn(self.N)

def time_assign_list_like_with_setitem(self):
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np.random.seed(1234)
self.df[list(range(100))] = np.random.randn(self.N, 100)


class ChainIndexing:

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1 change: 1 addition & 0 deletions doc/source/whatsnew/v1.2.0.rst
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Expand Up @@ -257,6 +257,7 @@ Other enhancements
- Improve numerical stability for :meth:`.Rolling.skew`, :meth:`.Rolling.kurt`, :meth:`Expanding.skew` and :meth:`Expanding.kurt` through implementation of Kahan summation (:issue:`6929`)
- Improved error reporting for subsetting columns of a :class:`.DataFrameGroupBy` with ``axis=1`` (:issue:`37725`)
- Implement method ``cross`` for :meth:`DataFrame.merge` and :meth:`DataFrame.join` (:issue:`5401`)
- Improve performance for :meth:`DataFrame.__setitem__` with list-like indexers (:issue:`37954`)
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.. ---------------------------------------------------------------------------

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14 changes: 3 additions & 11 deletions pandas/core/indexing.py
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Expand Up @@ -663,17 +663,9 @@ def _ensure_listlike_indexer(self, key, axis=None, value=None):
and not com.is_bool_indexer(key)
and all(is_hashable(k) for k in key)
):
for i, k in enumerate(key):
if k not in self.obj:
if value is None:
self.obj[k] = np.nan
elif is_array_like(value) and value.ndim == 2:
# GH#37964 have to select columnwise in case of array
self.obj[k] = value[:, i]
elif is_list_like(value):
self.obj[k] = value[i]
else:
self.obj[k] = value
keys = self.obj.columns.tolist()
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can you create the keys in the same order whether they are in the obj or not (e.g. combine L666 and 667)

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do we have a test for this ordering?

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Union should do the trick.

At least the test added with #37964 covers this

keys.extend([k for k in key if k not in self.obj])
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self.obj._mgr = self.obj._mgr.reindex_axis(keys, 0)

def __setitem__(self, key, value):
if isinstance(key, tuple):
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