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BUG: groupby then resample on column gives incorrect results if the index is out of order #59408

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BUG: groupby then resample on column gives incorrect results if the index is out of order #59408

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c21c5c9
Index should be ignored when using the on keyword argument to resample
aram-cedarwood Aug 4, 2024
626b722
add test for when index is set from column
aram-cedarwood Aug 10, 2024
70d6ee8
minor: change test function name
aram-cedarwood Aug 10, 2024
5d77941
add test case
aram-cedarwood Aug 10, 2024
c92ec0b
move reset_index
aram-cedarwood Aug 13, 2024
1ef4d3b
minor: add GH issue number to tests
aram-cedarwood Aug 13, 2024
55fe96b
add test
aram-cedarwood Aug 17, 2024
13f7414
Merge branch 'main' into groupby-then-resample-if-index-out-of-order
aram-cedarwood Aug 23, 2024
10836a2
push reset_index to _set_grouper
aram-cedarwood Aug 28, 2024
62bdbdf
simplify
aram-cedarwood Aug 28, 2024
dd566f1
Merge branch 'main' into groupby-then-resample-if-index-out-of-order
aram-cedarwood Sep 4, 2024
7a0ad97
remove tests per comments
aram-cedarwood Sep 4, 2024
612e275
Merge branch 'main' into groupby-then-resample-if-index-out-of-order
aram-cedarwood Oct 27, 2024
bd91de4
Merge branch 'main' into groupby-then-resample-if-index-out-of-order
aram-cedarwood Nov 16, 2024
8a7f662
change test_groupby_resample_on_api_with_getitem
aram-cedarwood Nov 26, 2024
9852678
Merge branch 'main' into groupby-then-resample-if-index-out-of-order
aram-cedarwood Mar 8, 2025
7777766
add comments
Apr 9, 2025
f784a3d
Merge branch 'main' into groupby-then-resample-if-index-out-of-order
Apr 9, 2025
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1 change: 1 addition & 0 deletions doc/source/whatsnew/v3.0.0.rst
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Expand Up @@ -121,6 +121,7 @@ These improvements also fixed certain bugs in groupby:
- :meth:`.DataFrameGroupBy.agg` would fail when there are multiple groupings, unobserved groups, and ``as_index=False`` (:issue:`36698`)
- :meth:`.DataFrameGroupBy.groups` with ``sort=False`` would sort groups; they now occur in the order they are observed (:issue:`56966`)
- :meth:`.DataFrameGroupBy.nunique` would fail when there are multiple groupings, unobserved groups, and ``as_index=False`` (:issue:`52848`)
- :meth:`.DataFrameGroupBy.resample` with an ``on`` value that is not ``None`` would have incorrect values when the index is out of order (:issue:`59350`)
- :meth:`.DataFrameGroupBy.sum` would have incorrect values when there are multiple groupings, unobserved groups, and non-numeric data (:issue:`43891`)
- :meth:`.DataFrameGroupBy.value_counts` would produce incorrect results when used with some categorical and some non-categorical groupings and ``observed=False`` (:issue:`56016`)

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6 changes: 5 additions & 1 deletion pandas/core/groupby/grouper.py
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Expand Up @@ -34,6 +34,7 @@
from pandas.core.indexes.api import (
Index,
MultiIndex,
RangeIndex,
default_index,
)
from pandas.core.series import Series
Expand Down Expand Up @@ -348,8 +349,11 @@ def _set_grouper(
reverse_indexer = self._indexer.argsort()
unsorted_ax = self._grouper.take(reverse_indexer)
ax = unsorted_ax.take(obj.index)
else:
elif isinstance(obj.index, RangeIndex):
ax = self._grouper.take(obj.index)
else:
# GH 59350
ax = self._grouper
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@rhshadrach rhshadrach Sep 3, 2024 •
edited
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What is the reason we need to do a .take in the RangeIndex case, but not otherwise?

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Hi, returning to this. I put in that condition to make this test pass: def test_groupby_resample_on_api_with_getitem(self): which was apparently added as part of #17813
I have not had a chance to look too deeply.

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Adding index=list("xyzwt") to the DataFrame in that test makes the op fail.

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It looks like the issue happens on pandas.core.resample:1559. We pass only the group x but the entire axis self.ax. I wonder if splitting the axis as we do data on L967 there and passing it to f would resolve.

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Hi @rhshadrach, coming back to this, sorry for the hiatus. Can you elaborate on the above please? (I think maybe the word "not" is missing somewhere; I'm not entirely sure what you mean.) What file are you referring to re: L967? Can you give me a link to a line?

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I did in my previous comment.

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It looks like the issue happens on pandas.core.resample:1559.

I think in your previous comment you provided a link for this ^

I wonder if splitting the axis as we do data on L967 there

I ask again because the link you provided in your previous comment does not contain data. Are you sure you didn't mean a different line here?

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Why does it need to contain data? We pass the func from the highlighted line to groupby, which has a DataSplitter. This splits data. My comment is that I wonder if we should be splitting axis as we do this data on L967.

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Thanks @rhshadrach for your patience. I am new to making changes to groupby.

  • By L967 you mean resample.py#L1577? (What is the significance of the number 967 in L967?)
  • Are you saying that the code you highlighted causes data to be split downstream? Can you please elaborate on how the data is split? It would help greatly.
  • Can you explain in greater detail how we should split axis?

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  • By L967 you mean resample.py#L1577? (What is the significance of the number 967 in L967?)

I'm not sure anymore and I doubt it would be helpful.

  • Can you please elaborate on how the data is split?

groupby splits data into groups and operates on each group. x in the code above is one of these groups, not the entire input data, while self.ax is the entire input's axis.

  • Can you explain in greater detail how we should split axis?

I would suggest determining first if this is the right direction to go before spending time on figuring out how to do it. As I've stated, I'm not sure this is the root cause of the issue (or even an issue at all!).

else:
if key not in obj._info_axis:
raise KeyError(f"The grouper name {key} is not found")
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243 changes: 243 additions & 0 deletions pandas/tests/resample/test_resampler_grouper.py
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Expand Up @@ -689,3 +689,246 @@ def test_groupby_resample_on_index_with_list_of_keys_missing_column():
rs = gb.resample("2D")
with pytest.raises(KeyError, match="Columns not found"):
rs[["val_not_in_dataframe"]]


def test_groupby_resample_after_set_index_and_not_on_column():
# GH 59350
df = DataFrame(
data={
"datetime": [
pd.to_datetime("2024-07-30T00:00Z"),
pd.to_datetime("2024-07-30T00:01Z"),
],
"group": ["A", "A"],
"numbers": [100, 200],
},
index=[1, 0],
).set_index("datetime")
gb = df.groupby("group")
rs = gb.resample("1min")
result = rs.aggregate({"numbers": "sum"})

index = pd.MultiIndex.from_arrays(
[
["A", "A"],
[pd.to_datetime("2024-07-30T00:00Z"), pd.to_datetime("2024-07-30T00:01Z")],
],
names=[
"group",
"datetime",
],
)
expected = DataFrame({"numbers": [100, 200]}, index=index)

tm.assert_frame_equal(result, expected)


@pytest.mark.parametrize(
"df",
[
DataFrame(
data={
"datetime": [
pd.to_datetime("2024-07-30T00:00Z"),
pd.to_datetime("2024-07-30T00:01Z"),
],
"group": ["A", "A"],
"numbers": [100, 200],
},
index=[1, 0],
),
DataFrame(
data={
"datetime": [
pd.to_datetime("2024-07-30T00:00Z"),
pd.to_datetime("2024-07-30T00:01Z"),
],
"group": ["A", "A"],
"numbers": [100, 200],
},
).set_index("group"),
DataFrame(
data={
"datetime": [
pd.to_datetime("2024-07-30T00:00Z"),
pd.to_datetime("2024-07-30T00:01Z"),
],
"group": ["A", "A"],
"numbers": [100, 200],
},
).set_index("datetime", drop=False),
],
)
def test_groupby_resample_on_column_when_index_is_unusual(df):
# GH 59350
gb = df.groupby("group")
rs = gb.resample("1min", on="datetime")
result = rs.aggregate({"numbers": "sum"})

index = pd.MultiIndex.from_arrays(
[
["A", "A"],
[pd.to_datetime("2024-07-30T00:00Z"), pd.to_datetime("2024-07-30T00:01Z")],
],
names=[
"group",
"datetime",
],
)
expected = DataFrame({"numbers": [100, 200]}, index=index)

tm.assert_frame_equal(result, expected)


def test_groupby_resample_then_groupby_is_reused_when_index_is_out_of_order():
# GH 59350
df = DataFrame(
data={
"datetime": [
pd.to_datetime("2024-07-30T00:00Z"),
pd.to_datetime("2024-07-30T00:01Z"),
],
"group": ["A", "A"],
"numbers": [100, 200],
},
index=[1, 0],
)

gb = df.groupby("group")

# use gb
result_1 = gb[["numbers"]].transform("sum")

index = Index([1, 0])
expected = DataFrame({"numbers": [300, 300]}, index=index)

tm.assert_frame_equal(result_1, expected)

# resample gb, unrelated to above
rs = gb.resample("1min", on="datetime")
result_2 = rs.aggregate({"numbers": "sum"})

index = pd.MultiIndex.from_arrays(
[
["A", "A"],
[pd.to_datetime("2024-07-30T00:00Z"), pd.to_datetime("2024-07-30T00:01Z")],
],
names=[
"group",
"datetime",
],
)
expected = DataFrame({"numbers": [100, 200]}, index=index)

tm.assert_frame_equal(result_2, expected)

# reuse gb, unrelated to above
result_3 = gb[["numbers"]].transform("sum")

tm.assert_frame_equal(result_1, result_3)


def test_groupby_resample_then_groupby_is_reused_when_index_is_set_from_column():
# GH 59350
df = DataFrame(
data={
"datetime": [
pd.to_datetime("2024-07-30T00:00Z"),
pd.to_datetime("2024-07-30T00:01Z"),
],
"group": ["A", "A"],
"numbers": [100, 200],
},
).set_index("group")

gb = df.groupby("group")

# use gb
result_1 = gb[["numbers"]].transform("sum")

index = Index(["A", "A"], name="group")
expected = DataFrame({"numbers": [300, 300]}, index=index)

tm.assert_frame_equal(result_1, expected)

# resample gb, unrelated to above
rs = gb.resample("1min", on="datetime")
result_2 = rs.aggregate({"numbers": "sum"})

index = pd.MultiIndex.from_arrays(
[
["A", "A"],
[pd.to_datetime("2024-07-30T00:00Z"), pd.to_datetime("2024-07-30T00:01Z")],
],
names=[
"group",
"datetime",
],
)
expected = DataFrame({"numbers": [100, 200]}, index=index)

tm.assert_frame_equal(result_2, expected)

# reuse gb, unrelated to above
result_3 = gb[["numbers"]].transform("sum")

tm.assert_frame_equal(result_1, result_3)


def test_groupby_resample_then_groupby_is_reused_when_groupby_selection_is_not_none():
# GH 59350
df = DataFrame(
data={
"datetime": [
pd.to_datetime("2024-07-30T00:00Z"),
pd.to_datetime("2024-07-30T00:01Z"),
],
"group": ["A", "A"],
"numbers": [100, 200],
},
index=[1, 0],
)

gb = df.groupby("group")
gb = gb[["numbers", "datetime"]] # gb._selection is ["numbers", "datetime"]

# use gb
result_1 = gb.transform("max")

index = Index([1, 0])
expected = DataFrame(
{
"numbers": [200, 200],
"datetime": [
pd.to_datetime("2024-07-30T00:01Z"),
pd.to_datetime("2024-07-30T00:01Z"),
],
},
index=index,
)

tm.assert_frame_equal(result_1, expected)

# resample gb, unrelated to above
rs = gb.resample("1min", on="datetime")
result_2 = rs.aggregate({"numbers": "sum"}) # Enter the `except IndexError:` block

index = pd.MultiIndex.from_arrays(
[
["A", "A"],
[pd.to_datetime("2024-07-30T00:00Z"), pd.to_datetime("2024-07-30T00:01Z")],
],
names=[
"group",
"datetime",
],
)
columns = pd.MultiIndex.from_arrays([["numbers"], ["numbers"]])
expected = DataFrame([[100], [200]], index=index, columns=columns)

tm.assert_frame_equal(result_2, expected)

# reuse gb, unrelated to above
result_3 = gb.transform("max")

tm.assert_frame_equal(result_1, result_3)