"OrderedHashTable" (Data Structure)

"OrderedHashTable"

represents a hash table where the keys and values are general expressions and the order in which keys are inserted is preserved.

Details

An ordered hash table is useful for storing individual values that can be retrieved by use of a key where it is important to preserve the order of insertion:

	CreateDataStructure["OrderedHashTable"]	create a new empty "OrderedHashTable"
	CreateDataStructure["OrderedHashTable",assoc]	create a new "OrderedHashTable" containing the rules from assoc
	Typed[x,"OrderedHashTable"]	give x the type "OrderedHashTable"

For a data structure of type "OrderedHashTable", the following operations can be used:

	ds["Copy"]	return a copy of ds	time: O(n)
	ds["Elements"]	return a list of the elements of ds	time: O(n)
	ds["EmptyQ"]	True, if ds has no elements	time: O(1)
	ds["Insert",keyvalue]	add key to ds with the associated value and return True if the addition succeeded	time: O(1)
	ds["KeyDrop",key]	drop key and its value from ds	time: O(1)
	ds["KeyDropAll"]	drop all the keys and their values from ds	time: O(n)
	ds["KeyExistsQ",key]	True, if the key exists in ds	time: O(1)
	ds["Keys"]	return the keys in ds as a list	time: O(n)
	ds["Length"]	the number of key-value pairs stored in ds	time: O(1)
	ds["Lookup",key]	return the value stored with key in ds; if the key is not found, return a Missing object	time: O(1)
	ds["Lookup",key,defFun]	return the value stored with key in ds; if the key is not found, return defFun[key]	time: O(1)
	ds["Values"]	return the values in ds as a list	time: O(n)
	ds["Visualization"]	return a visualization of ds	time: O(n)

The following functions are also supported:

	ds_i===ds_j	True, if ds_i equals ds_j
	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

Examples

open allclose all

Basic Examples (2)Summary of the most common use cases

A new "OrderedHashTable" can be created with CreateDataStructure:

In[1]:=1

✖

https://wolfram.com/xid/0b5m6os2ktjlyg95rs0yk8nbnyya-ck3oom

Out[1]=1

Insert a key with a value:

In[2]:=2

✖

https://wolfram.com/xid/0b5m6os2ktjlyg95rs0yk8nbnyya-84r1md

There is one key stored:

In[3]:=3

✖

https://wolfram.com/xid/0b5m6os2ktjlyg95rs0yk8nbnyya-tnm4iz

Out[3]=3

Test if a key is present:

In[4]:=4

✖

https://wolfram.com/xid/0b5m6os2ktjlyg95rs0yk8nbnyya-kfcutb

Out[4]=4

Look up a value:

In[5]:=5

✖

https://wolfram.com/xid/0b5m6os2ktjlyg95rs0yk8nbnyya-2ymbbr

Out[5]=5

When a key is not found, a Missing object is returned:

In[6]:=6

✖

https://wolfram.com/xid/0b5m6os2ktjlyg95rs0yk8nbnyya-3dkxgf

Out[6]=6

Return an expression version of ds:

In[7]:=7

✖

https://wolfram.com/xid/0b5m6os2ktjlyg95rs0yk8nbnyya-dbekgb

Out[7]=7

A visualization of the data structure can be generated:

In[1]:=1

✖

https://wolfram.com/xid/0b5m6os2ktjlyg95rs0yk8nbnyya-mfljzp

Out[1]=1

The order of insertions is preserved:

In[2]:=2

✖

https://wolfram.com/xid/0b5m6os2ktjlyg95rs0yk8nbnyya-mancrg

Out[2]=2

Scope (1)Survey of the scope of standard use cases

Information (1)

A new "OrderedHashTable" can be created with CreateDataStructure:

In[1]:=1

✖

https://wolfram.com/xid/0b5m6os2ktjlyg95rs0yk8nbnyya-j0wiym

Out[1]=1

Information about the data structure ds:

In[2]:=2

✖

https://wolfram.com/xid/0b5m6os2ktjlyg95rs0yk8nbnyya-5du3om

Out[2]=2

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