Sets

Sets are collections containing an sorted list of distinct "keys". East sets are dynamically sized and can contain an arbitrary number of keys. Currently sets in East are restricted to contain only strings. Nonetheless, they are an important data structure for working with data and implementing efficient algorithms.

Set values and types

The East type for sets with keys of type T is SetType(T) (currently the only allowed T is StringType). The EDK accepts standard JavaScript Sets as values for SetType.

East type	Example value (JavaScript)	East object notation
SetType(StringType)	new Set([])	{}
SetType(StringType)	new Set(["a", "b", "c"])	{"a", "b", "c",}

Constructing sets

Sets are constructed with the NewSet expression (a bit like new Set(...) in JavaScript). The first argument to NewSet is the type of key that can be contained within the set (i.e. StringType). Subsequent to that, you can optionally provide a list of expressions to populate keys in the new set.

East function	Description	Example usage	Result
NewSet	Create a new empty set of strings	NewSet(StringType)	{}
NewSet	Create a new set with two strings	NewSet(StringType, [Const("a"), Const("b")])	{"a", "b",}

When values are inserted into a set, the set always remains in a sorted order.

Basic operations on sets

You can check whether a key is inside a set using In, and how many keys are in a set with Size.

You can modify sets by inserting or deleting keys. Sets in East are immutable. The input set will not be modified; instead a new one will be returned.

East function	Description	Example usage	Result
Size	Get the number of values in a set	Size(new Set(["a", "b"]))	2
In	Determine if a key is in a set	In(new Set(["a", "b", "c"]), "b")	true
Insert	Insert a key into a set	Insert(new Set(["a", "b"]), "c")	{"a", "b", "c",}
Delete	Delete a key from a set	Delete(new Set(["a", "b"]), "a")	{"b",}

Set operations

You can take the union, intersection or difference between sets using these East expressions.

East function	Description	Example usage	Result
Union	Combine keys from two sets	Union(new Set(["a", "b"]), new Set(["b", "c"]))	{"a", "b", "c",}
`Intersect	Find common keys in two sets	Intersect(new Set(["a", "b"]), new Set(["b", "c"]))	{"b",}
SetDiff	Find keys not in another set	SetDiff(new Set(["a", "b"]), new Set(["b", "c"]))	{"a",}
SymDiff	Find keys in either set but not both	SymDiff(new Set(["a", "b"]), new Set(["b", "c"]))	{"a", "c",}

Advanced set operations

You can apply complex logic to sets with with with Filter, FilterMap, ToSet and Reduce. These are covered in detail in later sections.

Equality and ordering

Two sets are equal if they contain the same number of keys, and each key in the first set is also in the second.

Ordering of sets is defined lexically. The first values are compared, then the second, until the end is reached. If one set is the "prefix" of another, then it is lesser.

Representation

Sets are represented in East's canonical JSON representation as JSON arrays. They are printed by Print in East's object notation with {} delimiters and comma seperated values (including a trailing comma).

Next steps

Continue to the next tutorial to understand how to use and manipulate dictionaries of data with East and Elara.