API / Belt / Hashmap

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.

Examples

RESCRIPT
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.

Examples

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

We can add elements to the collection:

Examples

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

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

t

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

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

id

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

The identity needed for making an empty hash map.

make

RESCRIPT
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.

Examples

RESCRIPT
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

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

Clears a hash table.

Examples

RESCRIPT
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

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

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

Examples

RESCRIPT
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

RESCRIPT
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.

Examples

RESCRIPT
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

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

Creates copy of a hash map.

Examples

RESCRIPT
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

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

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

Examples

RESCRIPT
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

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

Checks if x is bound in tbl.

Examples

RESCRIPT
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

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

If bound exists, removes it from the hash map.

Examples

RESCRIPT
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

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

Same as forEach but takes uncurried function.

forEach

RESCRIPT
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.

Examples

RESCRIPT
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

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

reduce

RESCRIPT
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.

Examples

RESCRIPT
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

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

Same as keepMapInPlace but takes uncurried function.

keepMapInPlace

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

Filters out values for which function f returned None.

Examples

RESCRIPT
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

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

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

Examples

RESCRIPT
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

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

Returns array of key value pairs.

Examples

RESCRIPT
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

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

Returns array of keys.

Examples

RESCRIPT
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

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

Returns array of values.

Examples

RESCRIPT
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

RESCRIPT
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.

Examples

RESCRIPT
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

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

Examples

RESCRIPT
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

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

Examples

RESCRIPT
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

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

Examples

RESCRIPT
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)