API / Belt / Belt_HashMap

Belt_HashMap

A mutable Hash map which allows customized hash behavior.

All data are parameterized by not its only type but also a unique identity in the time of initialization, so that two HashMaps of ints initialized with different hash functions will have different type.

For example:


type t = int
module I0 = unpack(Belt.Id.hashableU(~hash=(. a: t) => "&"(a, 0xff_ff), ~eq=(. a, b) => a == b))
let s0: t<_, string, _> = make(~hintSize=40, ~id=module(I0))

module I1 = unpack(Belt.Id.hashableU(~hash=(. a: t) => "&"(a, 0xff), ~eq=(. a, b) => a == b))
let s1: t<_, string, _> = make(~hintSize=40, ~id=module(I1))

The invariant must be held: for two elements who are equal, their hashed value should be the same

Here the compiler would infer s0 and s1 having different type so that it would not mix.


let s0: t<int, I0.identity>
let s1: t<int, I1.identity>

We can add elements to the collection:


let () = {
  add(s1, 0, "3")
  add(s1, 1, "3")
}

Since this is an mutable data strucure, s1 will contain two pairs.

Int

module Int = Belt_HashMapInt

Specalized when key type is int, more efficient than the generic type

String

module String = Belt_HashMapString

Specalized when key type is string, more efficient than the generic type

t

type t<'key, 'value, 'id>

The type of hash tables from type 'key to type 'value.

id

type id<'a, 'id> = Belt_Id.hashable<'a, 'id>

The identity needed for making an empty hash map.

make

let make: (~hintSize: int, ~id: id<'key, 'id>) => t<'key, 'value, 'id>

make(~hintSize=10, ~id) creates a new map by taking in the comparator and hintSize.

RES
module IntHash = Belt.Id.MakeHashable({
  type t = int
  let hash = a => a
  let eq = (a, b) => a == b
})

let hMap = Belt.HashMap.make(~hintSize=10, ~id=module(IntHash))

Belt.HashMap.set(hMap, 0, "a")

clear

let clear: t<'key, 'value, 'id> => unit

Clears a hash table.

RES
module IntHash = Belt.Id.MakeHashable({
  type t = int
  let hash = a => a
  let eq = (a, b) => a == b
})

let hMap = Belt.HashMap.fromArray([(1, "1")], ~id=module(IntHash))
Belt.HashMap.clear(hMap)
Belt.HashMap.isEmpty(hMap) == true

isEmpty

let isEmpty: t<'a, 'b, 'c> => bool

isEmpty(m) checks whether a hash map is empty.

RES
module IntHash = Belt.Id.MakeHashable({
  type t = int
  let hash = a => a
  let eq = (a, b) => a == b
})

Belt.HashMap.isEmpty(Belt.HashMap.fromArray([(1, "1")], ~id=module(IntHash))) == false

set

let set: (t<'key, 'value, 'id>, 'key, 'value) => unit

set(hMap, k, v) if k does not exist, add the binding k,v, otherwise, update the old value with the new v.

RES
module IntHash = Belt.Id.MakeHashable({
  type t = int
  let hash = a => a
  let eq = (a, b) => a == b
})

let s0 = Belt.HashMap.fromArray([(2, "2"), (1, "1"), (3, "3")], ~id=module(IntHash))

Belt.HashMap.set(s0, 2, "3")

Belt.HashMap.valuesToArray(s0) == ["1", "3", "3"]

copy

let copy: t<'key, 'value, 'id> => t<'key, 'value, 'id>

Creates copy of a hash map.

RES
module IntHash = Belt.Id.MakeHashable({
  type t = int
  let hash = a => a
  let eq = (a, b) => a == b
})

let s0 = Belt.HashMap.fromArray([(2, "2"), (1, "1"), (3, "3")], ~id=module(IntHash))
let s1 = Belt.HashMap.copy(s0)

Belt.HashMap.set(s0, 2, "3")

Belt.HashMap.get(s0, 2) != Belt.HashMap.get(s1, 2)

get

let get: (t<'key, 'value, 'id>, 'key) => option<'value>

Returns value bound under specific key. If values not exist returns None.

RES
module IntHash = Belt.Id.MakeHashable({
  type t = int
  let hash = a => a
  let eq = (a, b) => a == b
})

let s0 = Belt.HashMap.make(~hintSize=10, ~id=module(IntHash))
Belt.HashMap.set(s0, 1, "value1")

Belt.HashMap.get(s0, 1) == Some("value1")
Belt.HashMap.get(s0, 2) == None

has

let has: (t<'key, 'value, 'id>, 'key) => bool

Checks if x is bound in tbl.

RES
module IntHash = Belt.Id.MakeHashable({
  type t = int
  let hash = a => a
  let eq = (a, b) => a == b
})

let s0 = Belt.HashMap.make(~hintSize=10, ~id=module(IntHash))
Belt.HashMap.set(s0, 1, "value1")

Belt.HashMap.has(s0, 1) == true
Belt.HashMap.has(s0, 2) == false

remove

let remove: (t<'key, 'value, 'id>, 'key) => unit

If bound exists, removes it from the hash map.

RES
module IntHash = Belt.Id.MakeHashable({
  type t = int
  let hash = a => a
  let eq = (a, b) => a == b
})

let s0 = Belt.HashMap.make(~hintSize=10, ~id=module(IntHash))
Belt.HashMap.set(s0, 1, "value1")
Belt.HashMap.remove(s0, 1)
Belt.HashMap.has(s0, 1) == false

forEachU

let forEachU: (t<'key, 'value, 'id>, (. 'key, 'value) => unit) => unit

Same as forEach but takes uncurried function.

forEach

let forEach: (t<'key, 'value, 'id>, ('key, 'value) => unit) => unit

forEach(tbl, f) 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.

RES
module IntHash = Belt.Id.MakeHashable({
  type t = int
  let hash = a => a
  let eq = (a, b) => a == b
})

let s0 = Belt.HashMap.make(~hintSize=10, ~id=module(IntHash))
Belt.HashMap.set(s0, 1, "value1")
Belt.HashMap.forEach(s0, (key, value) => Js.log2(key, value))
// prints (1, "value1")

reduceU

let reduceU: (t<'key, 'value, 'id>, 'c, (. 'c, 'key, 'value) => 'c) => 'c

reduce

let reduce: (t<'key, 'value, 'id>, 'c, ('c, 'key, 'value) => 'c) => 'c

reduce(tbl, init, f) 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.

RES
module IntHash = Belt.Id.MakeHashable({
  type t = int
  let hash = a => a
  let eq = (a, b) => a == b
})

let s0 = Belt.HashMap.make(~hintSize=10, ~id=module(IntHash))
Belt.HashMap.set(s0, 1, "value1")
Belt.HashMap.set(s0, 2, "value2")

Belt.HashMap.reduce(s0, "", (acc, key, value) => acc ++ (", " ++ value)) == "value1, value2"

keepMapInPlaceU

let keepMapInPlaceU: (t<'key, 'value, 'id>, (. 'key, 'value) => option<'value>) => unit

Same as keepMapInPlace but takes uncurried function.

keepMapInPlace

let keepMapInPlace: (t<'key, 'value, 'id>, ('key, 'value) => option<'value>) => unit

Filters out values for which function f returned None.

RES
module IntHash = Belt.Id.MakeHashable({
  type t = int
  let hash = a => a
  let eq = (a, b) => a == b
})

let s0 = Belt.HashMap.make(~hintSize=10, ~id=module(IntHash))
Belt.HashMap.set(s0, 1, "value1")
Belt.HashMap.set(s0, 2, "value2")

Belt.HashMap.keepMapInPlace(s0, (key, value) => key == 1 ? None : Some(value))

size

let size: t<'a, 'b, 'c> => int

size(tbl) returns the number of bindings in tbl. It takes constant time.

RES
module IntHash = Belt.Id.MakeHashable({
  type t = int
  let hash = a => a
  let eq = (a, b) => a == b
})

let s0 = Belt.HashMap.make(~hintSize=10, ~id=module(IntHash))
Belt.HashMap.set(s0, 1, "value1")
Belt.HashMap.set(s0, 2, "value2")

Belt.HashMap.size(s0) == 2

toArray

let toArray: t<'key, 'value, 'id> => array<('key, 'value)>

Returns array of key value pairs.

RES
module IntHash = Belt.Id.MakeHashable({
  type t = int
  let hash = a => a
  let eq = (a, b) => a == b
})

let s0 = Belt.HashMap.make(~hintSize=10, ~id=module(IntHash))
Belt.HashMap.set(s0, 1, "value1")
Belt.HashMap.set(s0, 2, "value2")

Belt.HashMap.toArray(s0) == [(1, "value1"), (2, "value2")]

keysToArray

let keysToArray: t<'key, 'a, 'b> => array<'key>

Returns array of keys.

RES
module IntHash = Belt.Id.MakeHashable({
  type t = int
  let hash = a => a
  let eq = (a, b) => a == b
})

let s0 = Belt.HashMap.make(~hintSize=10, ~id=module(IntHash))
Belt.HashMap.set(s0, 1, "value1")
Belt.HashMap.set(s0, 2, "value2")

Belt.HashMap.keysToArray(s0) == [1, 2]

valuesToArray

let valuesToArray: t<'a, 'value, 'b> => array<'value>

Returns array of values.

RES
module IntHash = Belt.Id.MakeHashable({
  type t = int
  let hash = a => a
  let eq = (a, b) => a == b
})

let s0 = Belt.HashMap.make(~hintSize=10, ~id=module(IntHash))
Belt.HashMap.set(s0, 1, "value1")
Belt.HashMap.set(s0, 2, "value2")

Belt.HashMap.valuesToArray(s0) == ["value1", "value2"]

fromArray

let fromArray: (array<('key, 'value)>, ~id: id<'key, 'id>) => t<'key, 'value, 'id>

Creates new hash map from array of pairs.

Returns array of values.

RES
module IntHash = Belt.Id.MakeHashable({
  type t = int
  let hash = a => a
  let eq = (a, b) => a == b
})

let s0 = Belt.HashMap.fromArray([(1, "value1"), (2, "value2")], ~id=module(IntHash))
Belt.HashMap.toArray(s0) == [(1, "value1"), (2, "value2")]

mergeMany

let mergeMany: (t<'key, 'value, 'id>, array<('key, 'value)>) => unit

RES
module IntHash = Belt.Id.MakeHashable({
  type t = int
  let hash = a => a
  let eq = (a, b) => a == b
})

let hMap = Belt.HashMap.make(~hintSize=10, ~id=module(IntHash))
Belt.HashMap.mergeMany(hMap, [(1, "1"), (2, "2")])

getBucketHistogram

let getBucketHistogram: t<'a, 'b, 'c> => array<int>

RES
  module IntHash = Belt.Id.MakeHashable({
    type t = int
    let hash = a => a
    let eq = (a, b) => a == b
  })
  let hMap = Belt.HashMap.make(~hintSize=10, ~id=module(IntHash))
  Belt.HashMap.set(hMap, 1, "1")

  Belt.HashMap.getBucketHistogram(hMap)

logStats

let logStats: t<'a, 'b, 'c> => unit

RES
  module IntHash = Belt.Id.MakeHashable({
    type t = int
    let hash = a => a
    let eq = (a, b) => a == b
  })
  let hMap = Belt.HashMap.make(~hintSize=10, ~id=module(IntHash))
  Belt.HashMap.set(hMap, 1, "1")

  Belt.HashMap.logStats(hMap)