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)