11. Find Repeat Customers

Difficulty: Easy · Topics: Aggregations, Filtering & Selection

orders has one row per order line: order_id, customer_id, product and amount. An order can have several lines.

For every customer with at least 2 different orders, return customer_id, orders (distinct order ids), products (distinct products) and total (sum of amount).

Row order does not matter; column names must match. Your code is graded on 3 test cases, including hidden edge cases.

Sample data

orders

order_id	customer_id	product	amount
1	c1	pen	10
1	c1	ink	5
2	c1	pen	10
3	c2	book	300
4	c3	pen	10
5	c3	pen	10

Expected output

customer_id	orders	products	total
c1	2	2	25
c3	2	1	20

Hints

Hint 1

F.countDistinct("order_id") counts orders, not lines.

Hint 2

Aggregate first, then filter on the aggregated column (SQL's HAVING).

Hint 3

Several aggregates can go in one agg call.

Learn the concepts

• groupBy + agg · 3 min read. Aggregate rows per group: counts, sums, averages, and how count(*) differs from count(col).
• filter / where · 4 min read. Keep the rows that match a condition, and the null and operator traps that silently drop data.

PySpark functions you'll practise

• groupBy
• agg
• sum
• countDistinct
• filter

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Browse

Topics: Window Functions · Joins · Aggregations · Pivot, Unpivot & Rollup · Arrays · Null Handling · Conditional Logic · Dates · Filtering & Selection · Strings

Difficulty: Easy · Medium · Hard · PySpark interview roadmap · Learn · All problems