"OrderedHashSet" (Data Structure)


represents a set where the members are general expressions, membership is computed by using a hash function and the order in which members are inserted is preserved.


  • An ordered hash set is useful for efficient insertion and removal as well as membership testing where it is important to preserve the order of insertion:
  • CreateDataStructure["OrderedHashSet"]create a new empty "OrderedHashSet"
    CreateDataStructure["OrderedHashSet",elems]create a new "OrderedHashSet" containing elems
    Typed[x,"OrderedHashSet"]give x the type "OrderedHashSet"
  • For a data structure of type "OrderedHashSet", the following operations can be used:
  • ds["Complement",list]remove elements from ds that appear in listtime: O(n)
    ds["Copy"]return a copy of dstime: O(n)
    ds["Elements"]return a list of the elements of dstime: O(n)
    ds["EmptyQ"]True, if ds has no elementstime: O(1)
    ds["Delete",x]delete x from ds; return True if x was actually an elementtime: O(1)
    ds["DeleteAll"]delete all the elements from dstime: O(n)
    ds["Insert",x]add x to the set and return True if addition succeededtime: O(1)
    ds["Intersection",list]remove elements from ds that do not appear in listtime: O(n)
    ds["Length"]returns the number of elements stored in dstime: O(1)
    ds["MemberQ",x]True, if x is an element of dstime: O(1)
    ds["Pop"]remove an element from ds and return ittime: O(1)
    ds["Union",list]add elements to ds that appear in listtime: O(n)
    ds["Visualization"]return a visualization of dstime: O(n)
  • The following functions are also supported:
  • dsi===dsjTrue, if dsi equals dsj
    FullForm[ds]full form of ds
    Information[ds]information about ds
    InputForm[ds]input form of ds
    Normal[ds]convert ds to a normal expression


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Basic Examples  (2)

A new "OrderedHashSet" can be created with CreateDataStructure:

Insert into the set:

There is one element in the set:

Test if an expression is stored:

If an expression is not stored, False is returned:

Remove an element from the set. If something was actually removed, return True:

Return an expression version of ds:

It is fast to insert elements:

A visualization of the data structure can be generated:

The order in which elements are inserted is preserved:

Scope  (2)

Information  (1)

A new "OrderedHashSet" can be created with CreateDataStructure:

Information about the data structure ds:

Set Operations  (1)

"OrderedHashSet" supports some core set operations. A new empty "OrderedHashSet" can be created with CreateDataStructure:

Insert an element into ds:

The "Union" operation adds elements that were not originally in the data structure:

The "Complement" operation removes elements from the data structure:

The "Intersection" operation leaves common elements in the data structure: