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Organize customers, shops and bill lists
A flat customer–shop–category list can be regrouped hierarchically. At the top choose a customer; inside that customer choose a shop; inside that shop keep categories or item rows. The grouping can match the questions you want to ask.
REAL COURSE DATA · SORT, GROUP AND VERIFY
Customer → shop → bill summaries
Follow the selected procedure. Change a field, tie rule or weekday and explain why the result changes.
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Predict the next change. Keep track of which list level, field and position convention the procedure uses.
Our first hierarchy uses the 30 existing bill summaries: Customer → Store → list of BillNo values. Srivatsan has four bills across SV Stores and Sun General. This preserves a clear path back to each original bill and keeps one customer’s information together.
A list of shop names is different from a list of bill records. A summary’s MajorCategories field is not a complete item-by-item sequence. To analyze purchased item rows, use the original rows as in Week 5’s verified Bill 1 example. Do not expand a summary into invented purchases.
A flat representation and a nested representation can retain different information. Decide whether repeats represent repeated visits, repeated items or distinct categories. Keep identities and counts when they matter; nesting alone does not enforce uniqueness.
Try it yourself
Can one customer’s inner shop list have a different length from another’s?
Show explained answer
Yes. Inner lists need not have equal lengths.
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Does a hierarchy of bill IDs count purchased units?
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No. It counts or stores bills. Quantities require the bill’s item data.
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Why retain BillNo while regrouping?
Show explained answer
It identifies the original bill so omitted fields can be looked up later.