Left merge failed with message: ValueError: Length mismatch: Expected axis has 36 elements, new values have 32 elements

[anmyachev]

This is a consequence of faulty optimization: #6665.

Failed on 06699a8.

Reproducer:

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,size=(1000, 64)))
df2 = pd.DataFrame(np.random.randint(0,100,size=(1000, 64)))
execute(df1)
execute(df2)


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