Conditional merge in pandas

pandas_conditionnal_merge.py

import pandas as pd

def join_part(A, B, cond, left_on, right_on):
    C = A.merge(B, left_on=left_on, right_on=right_on, how="inner", copy=False)
    return C[cond].copy()

def conditional_join(A, B, cond, left_on, right_on, batch_size=50000):
    indices = range(0, len(A) + batch_size, batch_size)
    batches = (A.iloc[b_start : b_start + batch_size] for b_start in indices)
    merges = (join_part(subset, B, cond, left_on, right_on) for subset in batches)
    return pd.concat(merges)