averageBy

1/**
2 * Calculates the average of an array based on a selector function.
3 *
4 * @param arr - Array of items.
5 * @param fn - Function that returns a number from each item.
6 * @returns The average value, or 0 if array is empty.
7 */
8export function averageBy<T>(arr: T[], fn: (item: T) => number): number {
9  if (arr.length === 0) return 0;
10  return arr.reduce((sum, item) => sum + fn(item), 0) / arr.length;
11}

• Flexible Selector Function

  Accepts a callback to determine how numerical values are extracted, making it adaptable to various data structures.

• Type-Safe and Generic

  Uses TypeScript generics to ensure type safety across different array item types.

• Handles Empty Arrays Gracefully

  Returns 0 instead of NaN or throwing an error when the array is empty, promoting safer usage.

• Concise and Readable

  The implementation is straightforward and easy to understand, making it maintainable and less error-prone.

Tests | Examples

1test('averageBy - objects with numeric field', () => {
2  const data = [{ score: 10 }, { score: 20 }, { score: 30 }];
3  expect(averageBy(data, item => item.score)).toBe(20);
4});
5
6test('averageBy - empty array returns 0', () => {
7  expect(averageBy([], item => 1)).toBe(0);
8});
9
10test('averageBy - constant selector', () => {
11  expect(averageBy(['a', 'b', 'c'], () => 2)).toBe(2);
12});
13
14test('averageBy - computed values', () => {
15  const data = [1, 2, 3, 4];
16  expect(averageBy(data, x => x * 2)).toBe(5);
17});

Common Use Cases

• Calculating Average Scores or Ratings

  Compute average review ratings, test scores, or other metrics from structured data.

• Statistical Aggregation

  Useful in analytics dashboards or reporting tools to extract and average values from complex datasets.

• Financial Calculations

  Average prices, transaction values, or earnings across objects representing financial data.

• Data Normalization or Transformation

  Serve as part of a data pipeline to normalize datasets before further processing.

• UI Summaries and Visualizations

  Generate averages for summary widgets, charts, or progress bars based on dynamic data.