pandas merge and concat cheat sheet
SQL-style joins with merge, stacking frames with concat, and validating join keys.
INNER JOIN
LEFT JOIN
RIGHT JOIN
FULL JOIN
merge
Inner / left join
df.merge(depts, on="dept", how="left")
Different key names
orders.merge(customers, left_on="customer_id", right_on="id")
Anti-join with indicator
m = df.merge(depts, on="dept", how="left", indicator=True) m[m["_merge"] == "left_only"]
Guard against duplicates
df.merge(depts, on="dept", validate="many_to_one")
concat
Stack rows
pd.concat([df_2023, df_2024], ignore_index=True)
Side by side
pd.concat([a, b], axis=1)
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