NSSet and her sexy daughter, NSMutableSet are officially my two favorite Cocoa classes. They have reached previously unmeasured levels of exquisitude. Sure, they have their faults, like being finite (I was hoping to prove the continuum hypothesis with NSSet--that's a math joke), but what they lack in nonsensical mathematical jargon, they make up for in usefulitude.
I call it, JSSet! A finite, well ordered, mutable set! Here's a quick rundown (you'll notice I took the liberty of adding some functions even NSSet can't match):
add(element) - Adds an element to the end of a set.
remove(element) - Removes an element from the set.
union(set) - Returns the union of two sets.
intersection(set) - Returns the intersection of two sets.
unionSet(set) - Unions this set with another.
intersectSet(set) - Intersects this set with another.
subtract(set) - Returns the relative complement.
subtractSet(set) - Removes the members of the set passed in.
symmetricDifference(set) - Returns the symmetric difference.
cartesianProduct(set) - Returns the cartesian product.
isSubset(set) - Determines if this set's elements are contained in another.
isSuperset(set) - Determines if this set contains another. This is not the same as the negation of isSubset().
isProperSubset(set) - Returns true if this set is a subset and not equal to another.
equals(set) - Returns true if and only if both sets are subsets of the other.
powerset(set) - Returns the powerset, or set of all sets, of this set.
walk(function) - Executes a function on each element. This does not affect the set's contents.
map(function) - Returns a new set by running each element through thr function passed in.
filter(function) - The elements for which the function evaluates to true are returned in a new set. The function should take the parameters item, index.
member(element) - Returns true for elements in the set.
slice(start, amount) - Returns a new set containing the elements from start through start + amount. If no amount is given, it will assume the largest possible amount.
print() - Prints all elements of the set using the console object.