Union By

mediumcodingJavaScriptArraysFunctions~25 min

Asked at Google, Meta, Amazon

Overview

Implement unionBy(iteratee, ...arrays) — returns a combined array with uniqueness determined by iteratee.

Examples

unionBy(Math.floor, [2.1, 1.2], [2.3, 3.4]); // [2.1, 1.2, 3.4]

Solution

Reveal solution

function unionBy(iteratee, ...arrays) {
  const seen = new Set();
  const result = [];
  for (const arr of arrays) {
    for (const item of arr) {
      const key = iteratee(item);
      if (!seen.has(key)) { seen.add(key); result.push(item); }
    }
  }
  return result;
}

union-by.js

Union By

mediumcodingJavaScriptArrays

Overview

Implement unionBy(iteratee, ...arrays) — returns a combined array with uniqueness determined by iteratee.

Examples

unionBy(Math.floor, [2.1, 1.2], [2.3, 3.4]); // [2.1, 1.2, 3.4]

Solution

Reveal solution

function unionBy(iteratee, ...arrays) {
  const seen = new Set();
  const result = [];
  for (const arr of arrays) {
    for (const item of arr) {
      const key = iteratee(item);
      if (!seen.has(key)) { seen.add(key); result.push(item); }
    }
  }
  return result;
}

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