Set Operations

set-operations.ts

/**
 * Returns the union of the two sets (`a ∪ b`),
 * i.e. all elements present in either set.
 */
export const union = <T>(a: Set<T>, b: Set<T>) => new Set(
    [...a].concat(...b)
)

/**
 * Returns the intersection of the two sets (`a ∩ b`),
 * i.e. only the elements contained in both sets.
 */
export const intersection = <T>(a: Set<T>, b: Set<T>) => new Set(
    [...a].filter((x) => b.has(x))
)

/**
 * Returns the difference between the two sets (`a - b`),
 * i.e. the elements contained in `a` but not in `b`.
 */
export const difference = <T>(a: Set<T>, b: Set<T>) => new Set(
    [...a].filter((x) => !b.has(x))
)

/**
 * Returns the symmetric difference between the two sets (`a Δ b`),
 * i.e. the elements contained in `a` but not in `b` and the elements
 * contained in `b` but not in `a`.
 */
export const symmetricDifference = <T>(a: Set<T>, b: Set<T>) => new Set(
    [...difference(a, b)].concat([...difference(b, a)])
)

/**
 * Returns `true` if `a` is a superset of `b` - `a ⊇ b`
 * i.e. if all values in `b` are also contained in `a`.
 */
export const isSuperset = <T>(a: Set<T>, b: Set<T>) =>
    [...b].every((x) => a.has(x))