The HashTable structure

The HashTable structure implements hash tables that are polymorphic in the key type.

The tables are implemented as an array of buckets, which are lists of key-value pairs. The number of buckets grows with the number of table entries.

Synopsis

structure HashTable

Interface

type ('a, 'b) hash_table

val mkTable : (('a -> word) * (('a * 'a) -> bool)) -> (int * exn)
      -> ('a,'b) hash_table

val clear : ('a, 'b) hash_table -> unit

val insert : ('a, 'b) hash_table -> ('a * 'b) -> unit

val inDomain : ('a, 'b) hash_table -> 'a -> bool

val lookup : ('a, 'b) hash_table -> 'a -> 'b

val find : ('a, 'b) hash_table -> 'a -> 'b option

val remove : ('a, 'b) hash_table -> 'a -> 'b

val numItems : ('a, 'b) hash_table ->  int

val listItems  : ('a, 'b) hash_table -> 'b list
val listItemsi : ('a, 'b) hash_table -> ('a * 'b) list

val app  : ('b -> unit) -> ('a, 'b) hash_table -> unit
val appi : (('a * 'b) -> unit) -> ('a, 'b) hash_table -> unit

val map  : ('b -> 'c) -> ('a, 'b) hash_table -> ('a, 'c) hash_table
val mapi : (('a * 'b) -> 'c) -> ('a, 'b) hash_table -> ('a, 'c) hash_table

val fold  : (('b *'c) -> 'c) -> 'c -> ('a, 'b) hash_table -> 'c
val foldi : (('a * 'b * 'c) -> 'c) -> 'c -> ('a, 'b) hash_table -> 'c

val modify  : ('b -> 'b) -> ('a, 'b) hash_table -> unit
val modifyi : (('a * 'b) -> 'b) -> ('a, 'b) hash_table -> unit

val filter  : ('b -> bool) -> ('a, 'b) hash_table -> unit
val filteri : (('a * 'b) -> bool) -> ('a, 'b) hash_table -> unit

val copy : ('a, 'b) hash_table -> ('a, 'b) hash_table

val bucketSizes : ('a, 'b) hash_table -> int list

Description

type ('a, 'b) hash_table

The type of imperative hash tables indexed by 'a values

val mkTable : 'a -> word) * (('a * 'a) -> bool -> (int * exn) -> ('a,'b) hash_table

mkTable (hash, same) (n, ex) creates a new hash table that uses the hash function to compute hash values for keys and the same function to test key equality. The table will be initially sized to hold at least n items. The exception ex is raised by the lookup and remove functions when the search key is not in the domain.

val clear : ('a, 'b) hash_table -> unit

clear tbl removes all of the entries in the table.

val insert : ('a, 'b) hash_table -> ('a * 'b) -> unit

insert tbl (key, item) inserts a mapping from key to item into tbl. Any existing mapping of key is discarded.

val inDomain : ('a, 'b) hash_table -> 'a -> bool

inDomain tbl key returns true if, and only if, key is in the domain of the table

val lookup : ('a, 'b) hash_table -> 'a -> 'b

lookup tbl key returns the item that key maps to if key is in the domain of tbl. Otherwise, the table’s exception is raised.

val find : ('a, 'b) hash_table -> 'a -> 'b option

find tbl key returns the SOME v if key is mapped to v in tbl. Otherwise, it returns NONE.

val remove : ('a, 'b) hash_table -> 'a -> 'b

remove tbl key returns the item that key maps to if key is in the domain of tbl and removes it from the table. Otherwise, the table’s exception is raised.

val numItems : ('a, 'b) hash_table -> int

numItems tbl returns the number of entries in the table.

val listItems : ('a, 'b) hash_table -> 'b list

listItems tbl returns a list of the items in the range of tbl.

val listItemsi : ('a, 'b) hash_table -> ('a * 'b) list

listItemsi tbl returns a list of the key-value entries in tbl.

val app : ('b -> unit) -> ('a, 'b) hash_table -> unit

app f tbl applies the function f to each item in the range of tbl.

val appi : (('a * 'b) -> unit) -> ('a, 'b) hash_table -> unit

appi f tbl applies the function f to each item in the key-value entries in tbl.

val map : ('b -> 'c) -> ('a, 'b) hash_table -> ('a, 'c) hash_table

map f tbl creates a new table with an entry (key, f(lookup tbl key)) in the new table for every key in tbl. The new table inherits its hash and key-equality functions, and exception from tbl.

val mapi : (('a * 'b) -> 'c) -> ('a, 'b) hash_table -> ('a, 'c) hash_table

mapi f tbl creates a new table with an entry (key, f(key, lookup tbl key)) in the new table for every key in tbl. The new table inherits its hash and key-equality functions, and exception from tbl.

val fold : (('b *'c) -> 'c) -> 'c -> ('a, 'b) hash_table -> 'c

fold f init tbl folds the function f over the items in the range of tbl using init as an initial value.

val foldi : (('a * 'b * 'c) -> 'c) -> 'c -> ('a, 'b) hash_table -> 'c

foldi f init tbl folds the function f over the key-velu entries in tbl using init as an initial value.

val modify : ('b -> 'b) -> ('a, 'b) hash_table -> unit

modify f tbl applies the function f for effect to the items in the range of tbl, replacing the old items with the result of applying f.

val modifyi : (('a * 'b) -> 'b) -> ('a, 'b) hash_table -> unit

modifyi f tbl applies the function f for effect to the key-value entries in tbl, replacing the old items with the result of applying f.

val filter : ('b -> bool) -> ('a, 'b) hash_table -> unit

filter pred tbl removes any entry (key, item) from tbl for which pred item returns false.

val filteri : (('a * 'b) -> bool) -> ('a, 'b) hash_table -> unit

filteri pred tbl removes any entry (key, item) from tbl for which pred(key, item) returns false.

val copy : ('a, 'b) hash_table -> ('a, 'b) hash_table

copy tbl creates a copy of tbl. This expression is equivalent to

map (fn x => x) tbl
val bucketSizes : ('a, 'b) hash_table -> int list

bucketSizes tbl returns a list of the current number of items per bucket. This function allows users to gauge the quality of their hashing function.

See Also