pandas groupby and pivot cheat sheet
Named aggregation, transform, pivot_table and crosstab patterns.
Groupby
Named aggregation
df.groupby("dept").agg(
people=("name", "count"),
avg_salary=("salary", "mean"),
)transform — keep row shape
df["dept_avg"] = df.groupby("dept")["salary"].transform("mean")Top N per group
df.sort_values("salary", ascending=False).groupby("dept").head(1)Reshaping
pivot_table
df.pivot_table(index="dept", columns="country", values="salary", aggfunc="mean")
crosstab
pd.crosstab(df["dept"], df["country"])
melt — wide to long
df.melt(id_vars="name", value_vars=["salary"])
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