mathjs/src/function/set/setUnion.js

import { flatten } from '../../utils/array.js'
import { factory } from '../../utils/factory.js'

const name = 'setUnion'
const dependencies = ['typed', 'size', 'concat', 'subset', 'setIntersect', 'setSymDifference', 'Index']

export const createSetUnion = /* #__PURE__ */ factory(name, dependencies, ({ typed, size, concat, subset, setIntersect, setSymDifference, Index }) => {
  /**
   * Create the union of two (multi)sets.
   * Multi-dimension arrays will be converted to single-dimension arrays before the operation.
   *
   * Syntax:
   *
   *    math.setUnion(set1, set2)
   *
   * Examples:
   *
   *    math.setUnion([1, 2, 3, 4], [3, 4, 5, 6])            // returns [1, 2, 3, 4, 5, 6]
   *    math.setUnion([[1, 2], [3, 4]], [[3, 4], [5, 6]])    // returns [1, 2, 3, 4, 5, 6]
   *
   * See also:
   *
   *    setIntersect, setDifference
   *
   * @param {Array | Matrix}    a1  A (multi)set
   * @param {Array | Matrix}    a2  A (multi)set
   * @return {Array | Matrix}    The union of two (multi)sets
   */
  return typed(name, {
    'Array | Matrix, Array | Matrix': function (a1, a2) {
      if (subset(size(a1), new Index(0)) === 0) { // if any of them is empty, return the other one
        return flatten(a2)
      } else if (subset(size(a2), new Index(0)) === 0) {
        return flatten(a1)
      }
      const b1 = flatten(a1)
      const b2 = flatten(a2)
      return concat(setSymDifference(b1, b2), setIntersect(b1, b2))
    }
  })
})