Class MultiSet

packages/db-ivm/src/multiset.ts:14–221

 * A multiset of data.
 */
export class MultiSet<T> {
  #inner: MultiSetArray<T>

  constructor(data: MultiSetArray<T> = []) {
    this.#inner = data
  }

  toString(indent = false): string {
    return `MultiSet(${JSON.stringify(this.#inner, null, indent ? 2 : undefined)})`
  }

  toJSON(): string {
    return JSON.stringify(Array.from(this.getInner()))
  }

  static fromJSON<U>(json: string): MultiSet<U> {
    return new MultiSet(JSON.parse(json))
  }

  /**
   * Apply a function to all records in the collection.
   */
  map<U>(f: (data: T) => U): MultiSet<U> {
    return new MultiSet(
      this.#inner.map(([data, multiplicity]) => [f(data), multiplicity]),
    )
  }

  /**
   * Filter out records for which a function f(record) evaluates to False.
   */
  filter(f: (data: T) => boolean): MultiSet<T> {
    return new MultiSet(this.#inner.filter(([data, _]) => f(data)))
  }

  /**
   * Negate all multiplicities in the collection.
   */
  negate(): MultiSet<T> {
    return new MultiSet(
      this.#inner.map(([data, multiplicity]) => [data, -multiplicity]),
    )
  }

  /**
   * Concatenate two collections together.
   */
  concat(other: MultiSet<T>): MultiSet<T> {
    const out: MultiSetArray<T> = []
    chunkedArrayPush(out, this.#inner)
    chunkedArrayPush(out, other.getInner())
    return new MultiSet(out)
  }

  /**
   * Produce as output a collection that is logically equivalent to the input
   * but which combines identical instances of the same record into one
   * (record, multiplicity) pair.