R: Class "hash"

hash-class {hash} | R Documentation

## Class "hash"

### Description

Implements a S4 hash class in R similar to hashes / associatesd 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")

[Package hash version 2.2.6 Index]