Data Wrangling with Python Datatable - Transformations Within a GroupBy

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Task: Group data by Date and Zip and get the ratio of Price to maximum Price per group.

from datatable import dt, f, update, by

df = dt.Frame(
    {
        "Date": ["2019-01-01", "2019-01-01", "2019-01-01", "2019-01-01", "2019-01-01"],
        "Zip": [90102, 90102, 90102, 90102, 90103],
        "Price": [58.02, 81.55, 11.97, 93.23, 13.68],
    }
)


df

	Date	Zip	Price
	▪▪▪▪	▪▪▪▪	▪▪▪▪▪▪▪▪
0	2019-01-01	90102	58.02
1	2019-01-01	90102	81.55
2	2019-01-01	90102	11.97
3	2019-01-01	90102	93.23
4	2019-01-01	90103	13.68

5 rows × 3 columns

SOLUTION

df[:, update(Ratio=f.Price / f.Price.max()), by("Date", "Zip")]
df

	Date	Zip	Price	Ratio
	▪▪▪▪	▪▪▪▪	▪▪▪▪▪▪▪▪	▪▪▪▪▪▪▪▪
0	2019-01-01	90102	58.02	0.622332
1	2019-01-01	90102	81.55	0.874718
2	2019-01-01	90102	11.97	0.128392
3	2019-01-01	90102	93.23	1
4	2019-01-01	90103	13.68	1

5 rows × 4 columns

Resources:

• update

• Grouping with by documentation

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