FEAT-#7254: Support right merge/join

[local-dev-korbit-ai-mentor]

What do these changes do?

Blocked on modin-project/modin#7251

Performance: 1.7 sec (the PR) vs 3.1 sec (on main) on Ray (8 cores)

import modin.pandas as pd
from time import time
import numpy as np
from modin.utils import execute

np.random.seed(42)

df1 = pd.DataFrame(np.random.randint(0, 100_000,size=(400_000, 64)))
df2 = pd.DataFrame(np.random.randint(0, 100_000,size=(400_000, 64)))
execute(df1)
execute(df2)


for _ in range(3):
    start = time()
    result = pd.merge(df1, df2, how="right", on=1)
    execute(result)
    print(f"{result.shape=}")
    print(f"merge time: {time()-start}")

• first commit message and PR title follow format outlined here

  NOTE: If you edit the PR title to match this format, you need to add another commit (even if it's empty) or amend your last commit for the CI job that checks the PR title to pick up the new PR title.

• passes flake8 modin/ asv_bench/benchmarks scripts/doc_checker.py
• passes black --check modin/ asv_bench/benchmarks scripts/doc_checker.py
• signed commit with git commit -s
• Resolves #7254
• tests added and passing
• module layout described at docs/development/architecture.rst is up-to-date

Description by Korbit AI

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What change is being made?

Add support for right merge/join in the row_axis_merge function within modin/core/storage_formats/pandas/merge.py.

Why are these changes being made?

The current implementation only supports left and inner joins, which limits functionality. Adding support for right joins enhances the flexibility and usability of the merge operations, addressing user needs for more comprehensive data manipulation capabilities.

Summary by CodeRabbit

• New Features

  • Enhanced merging logic for DataFrames with improved handling of "inner" merges when the left DataFrame has only one partition.

• Bug Fixes

  • Improved correctness of merged outputs by dynamically managing DataFrame order during merge operations.

[local-dev-korbit-ai-mentor]

Clone of the PR modin-project/modin#7226

[korbit-ai]

My review is in progress 📖 - I will have feedback for you in a few minutes!

[coderabbitai]

Caution

Review failed

The pull request is closed.

Walkthrough

The recent changes enhance the row_axis_merge function in Modin's merging logic, particularly for "inner" merges involving a single partition in the left DataFrame. By implementing a flexible handling of DataFrame order through a new boolean flag, the update improves the accuracy and efficiency of the merge operation, ensuring correct metadata computation and overall integrity of the output.

Changes

File Path	Change Summary
modin/core/storage_formats/pandas/merge.py	Enhanced row_axis_merge logic to manage DataFrame order more dynamically for "inner" merges. Added a reverted flag to adjust merge operations based on partition count.

Poem

In the meadow where data flows,
A merge now dances, as logic grows.
With partitions bright, and flags that play,
Inner joins shimmer in a new way.
Hop along, dear code, let the changes sing,
For in the world of data, joy they bring! 🐇✨

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[korbit-ai]

I have reviewed your code and did not find any issues!

---

Please note that I can make mistakes, and you should still encourage your team to review your code as well.

[furwellness]

/review

[codiumai-pr-agent-free]

PR Reviewer Guide 🔍

⏱️ Estimated effort to review: 3 🔵🔵🔵⚪⚪

🧪 PR contains tests

🔒 No security concerns identified

⚡ Key issues to review Code Duplication The code for computing result metadata is duplicated with slight variations for the reverted and non-reverted cases. This could be refactored to reduce duplication. Performance Concern The condition for swapping left and right dataframes is based on the shape of left._modin_frame._partitions. This might not always be the most efficient approach and could potentially lead to unexpected performance issues in certain scenarios.

[furwellness]

@coderabbitai review

[coderabbitai]

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