aoc-2022/venv/Lib/site-packages/pandas/tests/reshape/merge/test_multi.py

910 lines
29 KiB
Python

import numpy as np
import pytest
import pandas as pd
from pandas import (
DataFrame,
Index,
MultiIndex,
Series,
Timestamp,
)
import pandas._testing as tm
from pandas.core.reshape.concat import concat
from pandas.core.reshape.merge import merge
@pytest.fixture
def left():
"""left dataframe (not multi-indexed) for multi-index join tests"""
# a little relevant example with NAs
key1 = ["bar", "bar", "bar", "foo", "foo", "baz", "baz", "qux", "qux", "snap"]
key2 = ["two", "one", "three", "one", "two", "one", "two", "two", "three", "one"]
data = np.random.randn(len(key1))
return DataFrame({"key1": key1, "key2": key2, "data": data})
@pytest.fixture
def right(multiindex_dataframe_random_data):
"""right dataframe (multi-indexed) for multi-index join tests"""
df = multiindex_dataframe_random_data
df.index.names = ["key1", "key2"]
df.columns = ["j_one", "j_two", "j_three"]
return df
@pytest.fixture
def left_multi():
return DataFrame(
{
"Origin": ["A", "A", "B", "B", "C"],
"Destination": ["A", "B", "A", "C", "A"],
"Period": ["AM", "AM", "IP", "AM", "OP"],
"TripPurp": ["hbw", "nhb", "hbo", "nhb", "hbw"],
"Trips": [1987, 3647, 2470, 4296, 4444],
},
columns=["Origin", "Destination", "Period", "TripPurp", "Trips"],
).set_index(["Origin", "Destination", "Period", "TripPurp"])
@pytest.fixture
def right_multi():
return DataFrame(
{
"Origin": ["A", "A", "B", "B", "C", "C", "E"],
"Destination": ["A", "B", "A", "B", "A", "B", "F"],
"Period": ["AM", "AM", "IP", "AM", "OP", "IP", "AM"],
"LinkType": ["a", "b", "c", "b", "a", "b", "a"],
"Distance": [100, 80, 90, 80, 75, 35, 55],
},
columns=["Origin", "Destination", "Period", "LinkType", "Distance"],
).set_index(["Origin", "Destination", "Period", "LinkType"])
@pytest.fixture
def on_cols_multi():
return ["Origin", "Destination", "Period"]
@pytest.fixture
def idx_cols_multi():
return ["Origin", "Destination", "Period", "TripPurp", "LinkType"]
class TestMergeMulti:
def test_merge_on_multikey(self, left, right, join_type):
on_cols = ["key1", "key2"]
result = left.join(right, on=on_cols, how=join_type).reset_index(drop=True)
expected = merge(left, right.reset_index(), on=on_cols, how=join_type)
tm.assert_frame_equal(result, expected)
result = left.join(right, on=on_cols, how=join_type, sort=True).reset_index(
drop=True
)
expected = merge(
left, right.reset_index(), on=on_cols, how=join_type, sort=True
)
tm.assert_frame_equal(result, expected)
@pytest.mark.parametrize("sort", [False, True])
def test_left_join_multi_index(self, sort):
icols = ["1st", "2nd", "3rd"]
def bind_cols(df):
iord = lambda a: 0 if a != a else ord(a)
f = lambda ts: ts.map(iord) - ord("a")
return f(df["1st"]) + f(df["3rd"]) * 1e2 + df["2nd"].fillna(0) * 1e4
def run_asserts(left, right, sort):
res = left.join(right, on=icols, how="left", sort=sort)
assert len(left) < len(res) + 1
assert not res["4th"].isna().any()
assert not res["5th"].isna().any()
tm.assert_series_equal(res["4th"], -res["5th"], check_names=False)
result = bind_cols(res.iloc[:, :-2])
tm.assert_series_equal(res["4th"], result, check_names=False)
assert result.name is None
if sort:
tm.assert_frame_equal(res, res.sort_values(icols, kind="mergesort"))
out = merge(left, right.reset_index(), on=icols, sort=sort, how="left")
res.index = np.arange(len(res))
tm.assert_frame_equal(out, res)
lc = list(map(chr, np.arange(ord("a"), ord("z") + 1)))
left = DataFrame(np.random.choice(lc, (5000, 2)), columns=["1st", "3rd"])
left.insert(1, "2nd", np.random.randint(0, 1000, len(left)))
i = np.random.permutation(len(left))
right = left.iloc[i].copy()
left["4th"] = bind_cols(left)
right["5th"] = -bind_cols(right)
right.set_index(icols, inplace=True)
run_asserts(left, right, sort)
# inject some nulls
left.loc[1::23, "1st"] = np.nan
left.loc[2::37, "2nd"] = np.nan
left.loc[3::43, "3rd"] = np.nan
left["4th"] = bind_cols(left)
i = np.random.permutation(len(left))
right = left.iloc[i, :-1]
right["5th"] = -bind_cols(right)
right.set_index(icols, inplace=True)
run_asserts(left, right, sort)
@pytest.mark.parametrize("sort", [False, True])
def test_merge_right_vs_left(self, left, right, sort):
# compare left vs right merge with multikey
on_cols = ["key1", "key2"]
merged_left_right = left.merge(
right, left_on=on_cols, right_index=True, how="left", sort=sort
)
merge_right_left = right.merge(
left, right_on=on_cols, left_index=True, how="right", sort=sort
)
# Reorder columns
merge_right_left = merge_right_left[merged_left_right.columns]
tm.assert_frame_equal(merged_left_right, merge_right_left)
def test_merge_multiple_cols_with_mixed_cols_index(self):
# GH29522
s = Series(
range(6),
MultiIndex.from_product([["A", "B"], [1, 2, 3]], names=["lev1", "lev2"]),
name="Amount",
)
df = DataFrame({"lev1": list("AAABBB"), "lev2": [1, 2, 3, 1, 2, 3], "col": 0})
result = merge(df, s.reset_index(), on=["lev1", "lev2"])
expected = DataFrame(
{
"lev1": list("AAABBB"),
"lev2": [1, 2, 3, 1, 2, 3],
"col": [0] * 6,
"Amount": range(6),
}
)
tm.assert_frame_equal(result, expected)
def test_compress_group_combinations(self):
# ~ 40000000 possible unique groups
key1 = tm.rands_array(10, 10000)
key1 = np.tile(key1, 2)
key2 = key1[::-1]
df = DataFrame({"key1": key1, "key2": key2, "value1": np.random.randn(20000)})
df2 = DataFrame(
{"key1": key1[::2], "key2": key2[::2], "value2": np.random.randn(10000)}
)
# just to hit the label compression code path
merge(df, df2, how="outer")
def test_left_join_index_preserve_order(self):
on_cols = ["k1", "k2"]
left = DataFrame(
{
"k1": [0, 1, 2] * 8,
"k2": ["foo", "bar"] * 12,
"v": np.array(np.arange(24), dtype=np.int64),
}
)
index = MultiIndex.from_tuples([(2, "bar"), (1, "foo")])
right = DataFrame({"v2": [5, 7]}, index=index)
result = left.join(right, on=on_cols)
expected = left.copy()
expected["v2"] = np.nan
expected.loc[(expected.k1 == 2) & (expected.k2 == "bar"), "v2"] = 5
expected.loc[(expected.k1 == 1) & (expected.k2 == "foo"), "v2"] = 7
tm.assert_frame_equal(result, expected)
result.sort_values(on_cols, kind="mergesort", inplace=True)
expected = left.join(right, on=on_cols, sort=True)
tm.assert_frame_equal(result, expected)
# test join with multi dtypes blocks
left = DataFrame(
{
"k1": [0, 1, 2] * 8,
"k2": ["foo", "bar"] * 12,
"k3": np.array([0, 1, 2] * 8, dtype=np.float32),
"v": np.array(np.arange(24), dtype=np.int32),
}
)
index = MultiIndex.from_tuples([(2, "bar"), (1, "foo")])
right = DataFrame({"v2": [5, 7]}, index=index)
result = left.join(right, on=on_cols)
expected = left.copy()
expected["v2"] = np.nan
expected.loc[(expected.k1 == 2) & (expected.k2 == "bar"), "v2"] = 5
expected.loc[(expected.k1 == 1) & (expected.k2 == "foo"), "v2"] = 7
tm.assert_frame_equal(result, expected)
result = result.sort_values(on_cols, kind="mergesort")
expected = left.join(right, on=on_cols, sort=True)
tm.assert_frame_equal(result, expected)
def test_left_join_index_multi_match_multiindex(self):
left = DataFrame(
[
["X", "Y", "C", "a"],
["W", "Y", "C", "e"],
["V", "Q", "A", "h"],
["V", "R", "D", "i"],
["X", "Y", "D", "b"],
["X", "Y", "A", "c"],
["W", "Q", "B", "f"],
["W", "R", "C", "g"],
["V", "Y", "C", "j"],
["X", "Y", "B", "d"],
],
columns=["cola", "colb", "colc", "tag"],
index=[3, 2, 0, 1, 7, 6, 4, 5, 9, 8],
)
right = DataFrame(
[
["W", "R", "C", 0],
["W", "Q", "B", 3],
["W", "Q", "B", 8],
["X", "Y", "A", 1],
["X", "Y", "A", 4],
["X", "Y", "B", 5],
["X", "Y", "C", 6],
["X", "Y", "C", 9],
["X", "Q", "C", -6],
["X", "R", "C", -9],
["V", "Y", "C", 7],
["V", "R", "D", 2],
["V", "R", "D", -1],
["V", "Q", "A", -3],
],
columns=["col1", "col2", "col3", "val"],
).set_index(["col1", "col2", "col3"])
result = left.join(right, on=["cola", "colb", "colc"], how="left")
expected = DataFrame(
[
["X", "Y", "C", "a", 6],
["X", "Y", "C", "a", 9],
["W", "Y", "C", "e", np.nan],
["V", "Q", "A", "h", -3],
["V", "R", "D", "i", 2],
["V", "R", "D", "i", -1],
["X", "Y", "D", "b", np.nan],
["X", "Y", "A", "c", 1],
["X", "Y", "A", "c", 4],
["W", "Q", "B", "f", 3],
["W", "Q", "B", "f", 8],
["W", "R", "C", "g", 0],
["V", "Y", "C", "j", 7],
["X", "Y", "B", "d", 5],
],
columns=["cola", "colb", "colc", "tag", "val"],
index=[3, 3, 2, 0, 1, 1, 7, 6, 6, 4, 4, 5, 9, 8],
)
tm.assert_frame_equal(result, expected)
result = left.join(right, on=["cola", "colb", "colc"], how="left", sort=True)
expected = expected.sort_values(["cola", "colb", "colc"], kind="mergesort")
tm.assert_frame_equal(result, expected)
def test_left_join_index_multi_match(self):
left = DataFrame(
[["c", 0], ["b", 1], ["a", 2], ["b", 3]],
columns=["tag", "val"],
index=[2, 0, 1, 3],
)
right = DataFrame(
[
["a", "v"],
["c", "w"],
["c", "x"],
["d", "y"],
["a", "z"],
["c", "r"],
["e", "q"],
["c", "s"],
],
columns=["tag", "char"],
).set_index("tag")
result = left.join(right, on="tag", how="left")
expected = DataFrame(
[
["c", 0, "w"],
["c", 0, "x"],
["c", 0, "r"],
["c", 0, "s"],
["b", 1, np.nan],
["a", 2, "v"],
["a", 2, "z"],
["b", 3, np.nan],
],
columns=["tag", "val", "char"],
index=[2, 2, 2, 2, 0, 1, 1, 3],
)
tm.assert_frame_equal(result, expected)
result = left.join(right, on="tag", how="left", sort=True)
expected2 = expected.sort_values("tag", kind="mergesort")
tm.assert_frame_equal(result, expected2)
# GH7331 - maintain left frame order in left merge
result = merge(left, right.reset_index(), how="left", on="tag")
expected.index = np.arange(len(expected))
tm.assert_frame_equal(result, expected)
def test_left_merge_na_buglet(self):
left = DataFrame(
{
"id": list("abcde"),
"v1": np.random.randn(5),
"v2": np.random.randn(5),
"dummy": list("abcde"),
"v3": np.random.randn(5),
},
columns=["id", "v1", "v2", "dummy", "v3"],
)
right = DataFrame(
{
"id": ["a", "b", np.nan, np.nan, np.nan],
"sv3": [1.234, 5.678, np.nan, np.nan, np.nan],
}
)
result = merge(left, right, on="id", how="left")
rdf = right.drop(["id"], axis=1)
expected = left.join(rdf)
tm.assert_frame_equal(result, expected)
def test_merge_na_keys(self):
data = [
[1950, "A", 1.5],
[1950, "B", 1.5],
[1955, "B", 1.5],
[1960, "B", np.nan],
[1970, "B", 4.0],
[1950, "C", 4.0],
[1960, "C", np.nan],
[1965, "C", 3.0],
[1970, "C", 4.0],
]
frame = DataFrame(data, columns=["year", "panel", "data"])
other_data = [
[1960, "A", np.nan],
[1970, "A", np.nan],
[1955, "A", np.nan],
[1965, "A", np.nan],
[1965, "B", np.nan],
[1955, "C", np.nan],
]
other = DataFrame(other_data, columns=["year", "panel", "data"])
result = frame.merge(other, how="outer")
expected = frame.fillna(-999).merge(other.fillna(-999), how="outer")
expected = expected.replace(-999, np.nan)
tm.assert_frame_equal(result, expected)
@pytest.mark.parametrize("klass", [None, np.asarray, Series, Index])
def test_merge_datetime_index(self, klass):
# see gh-19038
df = DataFrame(
[1, 2, 3], ["2016-01-01", "2017-01-01", "2018-01-01"], columns=["a"]
)
df.index = pd.to_datetime(df.index)
on_vector = df.index.year
if klass is not None:
on_vector = klass(on_vector)
expected = DataFrame({"a": [1, 2, 3], "key_1": [2016, 2017, 2018]})
result = df.merge(df, on=["a", on_vector], how="inner")
tm.assert_frame_equal(result, expected)
expected = DataFrame(
{"key_0": [2016, 2017, 2018], "a_x": [1, 2, 3], "a_y": [1, 2, 3]}
)
result = df.merge(df, on=[df.index.year], how="inner")
tm.assert_frame_equal(result, expected)
@pytest.mark.parametrize("merge_type", ["left", "right"])
def test_merge_datetime_multi_index_empty_df(self, merge_type):
# see gh-36895
left = DataFrame(
data={
"data": [1.5, 1.5],
},
index=MultiIndex.from_tuples(
[[Timestamp("1950-01-01"), "A"], [Timestamp("1950-01-02"), "B"]],
names=["date", "panel"],
),
)
right = DataFrame(
index=MultiIndex.from_tuples([], names=["date", "panel"]), columns=["state"]
)
expected_index = MultiIndex.from_tuples(
[[Timestamp("1950-01-01"), "A"], [Timestamp("1950-01-02"), "B"]],
names=["date", "panel"],
)
if merge_type == "left":
expected = DataFrame(
data={
"data": [1.5, 1.5],
"state": [None, None],
},
index=expected_index,
)
results_merge = left.merge(right, how="left", on=["date", "panel"])
results_join = left.join(right, how="left")
else:
expected = DataFrame(
data={
"state": [None, None],
"data": [1.5, 1.5],
},
index=expected_index,
)
results_merge = right.merge(left, how="right", on=["date", "panel"])
results_join = right.join(left, how="right")
tm.assert_frame_equal(results_merge, expected)
tm.assert_frame_equal(results_join, expected)
@pytest.fixture
def household(self):
household = DataFrame(
{
"household_id": [1, 2, 3],
"male": [0, 1, 0],
"wealth": [196087.3, 316478.7, 294750],
},
columns=["household_id", "male", "wealth"],
).set_index("household_id")
return household
@pytest.fixture
def portfolio(self):
portfolio = DataFrame(
{
"household_id": [1, 2, 2, 3, 3, 3, 4],
"asset_id": [
"nl0000301109",
"nl0000289783",
"gb00b03mlx29",
"gb00b03mlx29",
"lu0197800237",
"nl0000289965",
np.nan,
],
"name": [
"ABN Amro",
"Robeco",
"Royal Dutch Shell",
"Royal Dutch Shell",
"AAB Eastern Europe Equity Fund",
"Postbank BioTech Fonds",
np.nan,
],
"share": [1.0, 0.4, 0.6, 0.15, 0.6, 0.25, 1.0],
},
columns=["household_id", "asset_id", "name", "share"],
).set_index(["household_id", "asset_id"])
return portfolio
@pytest.fixture
def expected(self):
expected = (
DataFrame(
{
"male": [0, 1, 1, 0, 0, 0],
"wealth": [
196087.3,
316478.7,
316478.7,
294750.0,
294750.0,
294750.0,
],
"name": [
"ABN Amro",
"Robeco",
"Royal Dutch Shell",
"Royal Dutch Shell",
"AAB Eastern Europe Equity Fund",
"Postbank BioTech Fonds",
],
"share": [1.00, 0.40, 0.60, 0.15, 0.60, 0.25],
"household_id": [1, 2, 2, 3, 3, 3],
"asset_id": [
"nl0000301109",
"nl0000289783",
"gb00b03mlx29",
"gb00b03mlx29",
"lu0197800237",
"nl0000289965",
],
}
)
.set_index(["household_id", "asset_id"])
.reindex(columns=["male", "wealth", "name", "share"])
)
return expected
def test_join_multi_levels(self, portfolio, household, expected):
portfolio = portfolio.copy()
household = household.copy()
# GH 3662
# merge multi-levels
result = household.join(portfolio, how="inner")
tm.assert_frame_equal(result, expected)
def test_join_multi_levels_merge_equivalence(self, portfolio, household, expected):
portfolio = portfolio.copy()
household = household.copy()
# equivalency
result = merge(
household.reset_index(),
portfolio.reset_index(),
on=["household_id"],
how="inner",
).set_index(["household_id", "asset_id"])
tm.assert_frame_equal(result, expected)
def test_join_multi_levels_outer(self, portfolio, household, expected):
portfolio = portfolio.copy()
household = household.copy()
result = household.join(portfolio, how="outer")
expected = concat(
[
expected,
(
DataFrame(
{"share": [1.00]},
index=MultiIndex.from_tuples(
[(4, np.nan)], names=["household_id", "asset_id"]
),
)
),
],
axis=0,
sort=True,
).reindex(columns=expected.columns)
tm.assert_frame_equal(result, expected)
def test_join_multi_levels_invalid(self, portfolio, household):
portfolio = portfolio.copy()
household = household.copy()
# invalid cases
household.index.name = "foo"
with pytest.raises(
ValueError, match="cannot join with no overlapping index names"
):
household.join(portfolio, how="inner")
portfolio2 = portfolio.copy()
portfolio2.index.set_names(["household_id", "foo"])
with pytest.raises(ValueError, match="columns overlap but no suffix specified"):
portfolio2.join(portfolio, how="inner")
def test_join_multi_levels2(self):
# some more advanced merges
# GH6360
household = DataFrame(
{
"household_id": [1, 2, 2, 3, 3, 3, 4],
"asset_id": [
"nl0000301109",
"nl0000301109",
"gb00b03mlx29",
"gb00b03mlx29",
"lu0197800237",
"nl0000289965",
np.nan,
],
"share": [1.0, 0.4, 0.6, 0.15, 0.6, 0.25, 1.0],
},
columns=["household_id", "asset_id", "share"],
).set_index(["household_id", "asset_id"])
log_return = DataFrame(
{
"asset_id": [
"gb00b03mlx29",
"gb00b03mlx29",
"gb00b03mlx29",
"lu0197800237",
"lu0197800237",
],
"t": [233, 234, 235, 180, 181],
"log_return": [
0.09604978,
-0.06524096,
0.03532373,
0.03025441,
0.036997,
],
}
).set_index(["asset_id", "t"])
expected = (
DataFrame(
{
"household_id": [2, 2, 2, 3, 3, 3, 3, 3],
"asset_id": [
"gb00b03mlx29",
"gb00b03mlx29",
"gb00b03mlx29",
"gb00b03mlx29",
"gb00b03mlx29",
"gb00b03mlx29",
"lu0197800237",
"lu0197800237",
],
"t": [233, 234, 235, 233, 234, 235, 180, 181],
"share": [0.6, 0.6, 0.6, 0.15, 0.15, 0.15, 0.6, 0.6],
"log_return": [
0.09604978,
-0.06524096,
0.03532373,
0.09604978,
-0.06524096,
0.03532373,
0.03025441,
0.036997,
],
}
)
.set_index(["household_id", "asset_id", "t"])
.reindex(columns=["share", "log_return"])
)
# this is the equivalency
result = merge(
household.reset_index(),
log_return.reset_index(),
on=["asset_id"],
how="inner",
).set_index(["household_id", "asset_id", "t"])
tm.assert_frame_equal(result, expected)
expected = (
DataFrame(
{
"household_id": [1, 2, 2, 2, 2, 3, 3, 3, 3, 3, 3, 4],
"asset_id": [
"nl0000301109",
"nl0000301109",
"gb00b03mlx29",
"gb00b03mlx29",
"gb00b03mlx29",
"gb00b03mlx29",
"gb00b03mlx29",
"gb00b03mlx29",
"lu0197800237",
"lu0197800237",
"nl0000289965",
None,
],
"t": [
None,
None,
233,
234,
235,
233,
234,
235,
180,
181,
None,
None,
],
"share": [
1.0,
0.4,
0.6,
0.6,
0.6,
0.15,
0.15,
0.15,
0.6,
0.6,
0.25,
1.0,
],
"log_return": [
None,
None,
0.09604978,
-0.06524096,
0.03532373,
0.09604978,
-0.06524096,
0.03532373,
0.03025441,
0.036997,
None,
None,
],
}
)
.set_index(["household_id", "asset_id", "t"])
.reindex(columns=["share", "log_return"])
)
result = merge(
household.reset_index(),
log_return.reset_index(),
on=["asset_id"],
how="outer",
).set_index(["household_id", "asset_id", "t"])
tm.assert_frame_equal(result, expected)
class TestJoinMultiMulti:
def test_join_multi_multi(
self, left_multi, right_multi, join_type, on_cols_multi, idx_cols_multi
):
# Multi-index join tests
expected = (
merge(
left_multi.reset_index(),
right_multi.reset_index(),
how=join_type,
on=on_cols_multi,
)
.set_index(idx_cols_multi)
.sort_index()
)
result = left_multi.join(right_multi, how=join_type).sort_index()
tm.assert_frame_equal(result, expected)
def test_join_multi_empty_frames(
self, left_multi, right_multi, join_type, on_cols_multi, idx_cols_multi
):
left_multi = left_multi.drop(columns=left_multi.columns)
right_multi = right_multi.drop(columns=right_multi.columns)
expected = (
merge(
left_multi.reset_index(),
right_multi.reset_index(),
how=join_type,
on=on_cols_multi,
)
.set_index(idx_cols_multi)
.sort_index()
)
result = left_multi.join(right_multi, how=join_type).sort_index()
tm.assert_frame_equal(result, expected)
@pytest.mark.parametrize("box", [None, np.asarray, Series, Index])
def test_merge_datetime_index(self, box):
# see gh-19038
df = DataFrame(
[1, 2, 3], ["2016-01-01", "2017-01-01", "2018-01-01"], columns=["a"]
)
df.index = pd.to_datetime(df.index)
on_vector = df.index.year
if box is not None:
on_vector = box(on_vector)
expected = DataFrame({"a": [1, 2, 3], "key_1": [2016, 2017, 2018]})
result = df.merge(df, on=["a", on_vector], how="inner")
tm.assert_frame_equal(result, expected)
expected = DataFrame(
{"key_0": [2016, 2017, 2018], "a_x": [1, 2, 3], "a_y": [1, 2, 3]}
)
result = df.merge(df, on=[df.index.year], how="inner")
tm.assert_frame_equal(result, expected)
def test_single_common_level(self):
index_left = MultiIndex.from_tuples(
[("K0", "X0"), ("K0", "X1"), ("K1", "X2")], names=["key", "X"]
)
left = DataFrame(
{"A": ["A0", "A1", "A2"], "B": ["B0", "B1", "B2"]}, index=index_left
)
index_right = MultiIndex.from_tuples(
[("K0", "Y0"), ("K1", "Y1"), ("K2", "Y2"), ("K2", "Y3")], names=["key", "Y"]
)
right = DataFrame(
{"C": ["C0", "C1", "C2", "C3"], "D": ["D0", "D1", "D2", "D3"]},
index=index_right,
)
result = left.join(right)
expected = merge(
left.reset_index(), right.reset_index(), on=["key"], how="inner"
).set_index(["key", "X", "Y"])
tm.assert_frame_equal(result, expected)
def test_join_multi_wrong_order(self):
# GH 25760
# GH 28956
midx1 = MultiIndex.from_product([[1, 2], [3, 4]], names=["a", "b"])
midx3 = MultiIndex.from_tuples([(4, 1), (3, 2), (3, 1)], names=["b", "a"])
left = DataFrame(index=midx1, data={"x": [10, 20, 30, 40]})
right = DataFrame(index=midx3, data={"y": ["foo", "bar", "fing"]})
result = left.join(right)
expected = DataFrame(
index=midx1,
data={"x": [10, 20, 30, 40], "y": ["fing", "foo", "bar", np.nan]},
)
tm.assert_frame_equal(result, expected)