hash-class {hash}

Class "hash"

Description

Implements a S4 hash class in R similar to hashes / associated arrays / dictionaries in other programming languages. Where possible, the hash class uses the standard R accessors: $, [ and [[. Hash construction is flexible and takes several syntaxes and all hash operations are supported.

For shorter key-value pairs, lists might yield higher performance, but for lists of appreciable length hash objects handly outperform native lists.

Slots

.xData:

Object of class "environment". This is the hashed environment used for key-value storage.

Extends

environment

Methods

HASH ACCESSORS:

[<-

signature(x = "hash", i = "ANY", j = "missing"): Slice Replacement

[

signature(x = "hash", i = "ANY", j = "missing", drop = "missing") : Slice

[[<-

signature(x = "hash", i = "ANY", j = "missing"): Single key replacement with interpolation.

[[

signature(x = "hash", i = "ANY", j = "missing"): i Single key look-up with interpolation

$<-

signature(x = "hash"): Single key replacement no interpolation

$

signature(x = "hash"): Single key lookup no interpolation

Manipulation:

clear

signature(x = "hash"): Remove all key-value pairs from hash

del

signature(x = "ANY", hash = "hash"): Remove specified key-value pairs from hash

has.key

signature(key = "ANY", hash = "hash"): Test for existence of key

is.empty

signature(x = "hash"): Test if no key-values are assigned

length

signature(x = "hash"): Return number of key-value pairs from the hash

keys

signature(hash = "hash"): Retrieve keys from hash

values

signature(x = "hash"): Retrieve values from hash

copy

signature(x = "hash"): Make a copy of a hash using a new environment.

format

signature(x = "hash"): Internal function for displaying hash

Note

HASH KEYS must be a valid character value and may not be the empty string "".

HASH VALUES can be any R value, vector or object.

PASS-BY REFERENCE. Environments and hashes are special objects in R because only one copy exists globally. When provide as an argument to a function, no local copy is made and any changes to the hash in the functions are reflected globally.

PERFORMANCE. Hashes are based on environments and are designed to be exceedingly fast using the environments internal hash table. For small data structures, a list will out-perform a hash in nearly every case. For larger data structure, i.e. >100-1000 key value pair the performance of the hash becomes faster. Much beyond that the performance of the hash far outperforms native lists.

MEMORY. Objects of class hash do not release memory with a call to rm. clear must be called before rm to properly release the memory.

Author(s)

Christopher Brown

References

http://en.wikipedia.org/wiki/Hash_table

http://en.wikipedia.org/wiki/Associative_array

See Also

hash-accessors, environment.

Examples

  showClass("hash")