Module BatHashtbl

module BatHashtbl: sig .. end

Extra functions over hashtables.

Operations over hashtables.

This module replaces Stdlib's Hashtbl module. All functions and types are provided here.

Base operations

val create : int -> ('a, 'b) Hashtbl.t

Hashtbl.create n creates a new, empty hash table, with initial size n. For best results, n should be on the order of the expected number of elements that will be in the table. The table grows as needed, so n is just an initial guess.

val length : ('a, 'b) Hashtbl.t -> int

Hashtbl.length tbl returns the number of bindings in tbl. Multiple bindings are counted multiply, so Hashtbl.length gives the number of times Hashtbl.iter calls its first argument.

val is_empty : ('a, 'b) Hashtbl.t -> bool

Hashtbl.is_empty tbl returns true if there are no bindings in tbl, false otherwise.

val add : ('a, 'b) Hashtbl.t -> 'a -> 'b -> unit

Hashtbl.add tbl x y adds a binding of x to y in table tbl. Previous bindings for x are not removed, but simply hidden. That is, after performing Hashtbl.remove tbl x, the previous binding for x, if any, is restored. (Same behavior as with association lists.)

val remove : ('a, 'b) Hashtbl.t -> 'a -> unit

Hashtbl.remove tbl x removes the current binding of x in tbl, restoring the previous binding if it exists. It does nothing if x is not bound in tbl.

val remove_all : ('a, 'b) Hashtbl.t -> 'a -> unit

Remove all bindings for the given key

val replace : ('a, 'b) Hashtbl.t -> 'a -> 'b -> unit

Hashtbl.replace tbl x y replaces the current binding of x in tbl by a binding of x to y. If x is unbound in tbl, a binding of x to y is added to tbl. This is functionally equivalent to Hashtbl.remove tbl x followed by Hashtbl.add tbl x y.

val copy : ('a, 'b) Hashtbl.t -> ('a, 'b) Hashtbl.t

Return a copy of the given hashtable.

val clear : ('a, 'b) Hashtbl.t -> unit

Empty a hash table.

Enumerations

val keys : ('a, 'b) Hashtbl.t -> 'a BatEnum.t

Return an enumeration of all the keys of a hashtable. If the key is in the Hashtable multiple times, all occurrences will be returned.

val values : ('a, 'b) Hashtbl.t -> 'b BatEnum.t

Return an enumeration of all the values of a hashtable.

val enum : ('a, 'b) Hashtbl.t -> ('a * 'b) BatEnum.t

Return an enumeration of (key,value) pairs of a hashtable.

val of_enum : ('a * 'b) BatEnum.t -> ('a, 'b) Hashtbl.t

Create a hashtable from a (key,value) enumeration.

Searching

val find : ('a, 'b) Hashtbl.t -> 'a -> 'b

Hashtbl.find tbl x returns the current binding of x in tbl, or raises Not_found if no such binding exists.

val find_all : ('a, 'b) Hashtbl.t -> 'a -> 'b list

Hashtbl.find_all tbl x returns the list of all data associated with x in tbl. The current binding is returned first, then the previous bindings, in reverse order of introduction in the table.

val find_default : ('a, 'b) Hashtbl.t -> 'a -> 'b -> 'b

Find a binding for the key, and return a default value if not found

val find_option : ('a, 'b) Hashtbl.t -> 'a -> 'b option

Find a binding for the key, or return None if no value is found

val mem : ('a, 'b) Hashtbl.t -> 'a -> bool

Hashtbl.mem tbl x checks if x is bound in tbl.

exists h k returns true is at least one item with key k is found in the hashtable.

Traversing

A number of higher-order functions are provided to allow purely functional traversal or transformation of hashtables. These functions are similar to their counterparts in module BatEnum.

Whenever you wish to traverse or transfor a hashtable, you have the choice between using the more general functions of BatEnum, with BatHashtbl.keys, BatHashtbl.values, BatHashtbl.enum and BatHashtbl.of_enum, or the more optimized functions of this section.

If you are new to OCaml or unsure about data structure, using the functions of BatEnum is a safe bet. Should you wish to improve performance at the cost of generality, you will always be able to rewrite your code to make use of the functions of this section.

val iter : ('a -> 'b -> unit) -> ('a, 'b) Hashtbl.t -> unit

Hashtbl.iter f tbl applies f to all bindings in table tbl. f receives the key as first argument, and the associated value as second argument. Each binding is presented exactly once to f. The order in which the bindings are passed to f is unspecified. However, if the table contains several bindings for the same key, they are passed to f in reverse order of introduction, that is, the most recent binding is passed first.

val fold : ('a -> 'b -> 'c -> 'c) -> ('a, 'b) Hashtbl.t -> 'c -> 'c

Hashtbl.fold f tbl init computes (f kN dN ... (f k1 d1 init)...), where k1 ... kN are the keys of all bindings in tbl, and d1 ... dN are the associated values. Each binding is presented exactly once to f. The order in which the bindings are passed to f is unspecified. However, if the table contains several bindings for the same key, they are passed to f in reverse order of introduction, that is, the most recent binding is passed first.

val map : ('a -> 'b -> 'c) -> ('a, 'b) Hashtbl.t -> ('a, 'c) Hashtbl.t

map f x creates a new hashtable with the same keys as x, but with the function f applied to all the values

val filter : ('a -> bool) -> ('b, 'a) Hashtbl.t -> ('b, 'a) Hashtbl.t

filter f m returns a new hashtable where only the values a of m such that f a = true remain.

val filteri : ('a -> 'b -> bool) -> ('a, 'b) Hashtbl.t -> ('a, 'b) Hashtbl.t

filter f m returns a map where only the key, values pairs key, a of m such that f key a = true remain. The bindings are passed to f in increasing order with respect to the ordering over the type of the keys.

val filter_map : ('a -> 'b -> 'c option) -> ('a, 'b) Hashtbl.t -> ('a, 'c) Hashtbl.t

filter_map f m combines the features of filteri and map. It calls calls f key0 a0, f key1 a1, f keyn an where a0..an are the elements of m and key0..keyn the respective corresponding keys. It returns the map of pairs keyi,bi such as f keyi ai = Some bi (when f returns None, the corresponding element of m is discarded).

The polymorphic hash primitive

val hash : 'a -> int

Hashtbl.hash x associates a positive integer to any value of any type. It is guaranteed that if x = y or Pervasives.compare x y = 0, then hash x = hash y. Moreover, hash always terminates, even on cyclic structures.

val hash_param : int -> int -> 'a -> int

Hashtbl.hash_param n m x computes a hash value for x, with the same properties as for hash. The two extra parameters n and m give more precise control over hashing. Hashing performs a depth-first, right-to-left traversal of the structure x, stopping after n meaningful nodes were encountered, or m nodes, meaningful or not, were encountered. Meaningful nodes are: integers; floating-point numbers; strings; characters; booleans; and constant constructors. Larger values of m and n means that more nodes are taken into account to compute the final hash value, and therefore collisions are less likely to happen. However, hashing takes longer. The parameters m and n govern the tradeoff between accuracy and speed.

Boilerplate code

Printing

val print : ?first:string ->
       ?last:string ->
       ?sep:string ->
       ('a BatInnerIO.output -> 'b -> unit) ->
       ('a BatInnerIO.output -> 'c -> unit) ->
       'a BatInnerIO.output -> ('b, 'c) Hashtbl.t -> unit

Override modules

The following modules replace functions defined in Hashtbl with functions behaving slightly differently but having the same name. This is by design: the functions meant to override the corresponding functions of Hashtbl.

module Exceptionless: sig .. end

Operations on Hashtbl without exceptions.

module Labels: sig .. end

Operations on Hashtbl with labels.

Functorial interface

module type HashedType = sig .. end

module type S = sig .. end

The output signature of the functor Hashtbl.Make.

module Make: functor (H : HashedType) -> S  with type key = H.t

Functor building an implementation of the hashtable structure.

module Cap: sig .. end

Capabilities for hashtables.