Mode Calculation

PySpark data engineering interview problem. Difficulty: intermediate. Pattern: Aggregation. About 16 minutes. Part of the Pro drill bank.

Most frequent amount value. Treat this as a production helper: match the contracted return shape, including empty and duplicate inputs.

The mode is the value that appears the most times. In a list of 10, 20, 10, 30, 10 and 20, the value 10 appears 3 times, more than any other. Return 1 row with the column mode_amount, the most common amount in df. If 2 values appear the same number of times, return the smaller one. The editor creates the table df and ends with result = df. Change the last line to build your answer. Count how many times each amount appears, then pick the amount with the highest count.

Requirements

• Count how many times each amount appears.
• Pick the amount with the highest count.
• When counts tie, pick the smaller amount.
• Return 1 row with mode_amount, and store it in result.

Constraints

• The table has 1 column, amount, with decimal values.
• The tie rule is part of the order: highest count first, then smallest amount.
• Return exactly 1 row.

Examples

Input: repeated amounts Output: mode_amount 10.0 10 appears 3 times.

Topics: lakebench, pyspark, mode, groupBy.

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