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Jaro-Winkler in F#

Jaro-Winkler is a fast and effective name matching algorithm. For more info see "A Comparison of String Distance Metrics for Name-Matching Tasks" http://www.isi.edu/info-agents/workshops/ijcai03/papers/Cohen-p.pdf or the Wikipedia article http://en.wikipedia.org/wiki/Jaro%E2%80%93Winkler_distance

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let windowAt str offset radius =
    let startAt = max 0 (offset - radius)
    let endAt = min (offset + radius) (String.length str - 1)  
    [ for i = startAt to endAt do yield str.[i] ]

let jaro s1 s2 = 
    let matchRadius = 
        let s1_l, s2_l = String.length s1, String.length s2 in
            (min s1_l s2_l) / 2 +
            (min s1_l s2_l) % 2

    let commonChars chars1 chars2 =
        [
            for i = 0 to String.length chars1 - 1 do
                let matchChar = chars1.[i]
                let windowChars = windowAt chars2 i matchRadius
                if windowChars |> List.exists (fun c -> c = matchChar) then
                    yield matchChar 
        ]
            
    let common1 = commonChars s1 s2
    let common2 = commonChars s2 s1

    let totalTranspositions = 
        List.zip common1 common2
        |> List.fold (fun s (c1,c2) -> if c1 <> c2 then s + 1.0 else s) 0.0
    let transpositions = totalTranspositions / 2.0

    let s1length = float (String.length s1)
    let s2length = float (String.length s2)
    let c1length = float (List.length common1)    
    let c2length = float (List.length common2)

    ((c1length / s1length) + (c2length / s2length) + ((c1length - transpositions) / c1length)) / 3.0


let jaroWinkler s1 s2 = 
    let jaroScore = jaro s1 s2
    let p = 0.1
    let maxLength = (min s1.Length s2.Length) - 1
    let rec calcL i acc =
        if i > maxLength || s1.[i] <> s2.[i] then acc
        else calcL (i + 1) (acc + 1.0)
    let l = calcL 0 0.0
    jaroScore + (l * p * (1.0 - jaroScore))

val windowAt : str:string -> offset:int -> radius:int -> char list

Full name: Script.windowAt

val str : string

val offset : int

val radius : int

val startAt : int

val max : e1:'T -> e2:'T -> 'T (requires comparison)

Full name: Microsoft.FSharp.Core.Operators.max

val endAt : int

val min : e1:'T -> e2:'T -> 'T (requires comparison)

Full name: Microsoft.FSharp.Core.Operators.min

module String

from Microsoft.FSharp.Core

val length : str:string -> int

Full name: Microsoft.FSharp.Core.String.length

val i : int

val jaro : s1:string -> s2:string -> float

Full name: Script.jaro

val s1 : string

val s2 : string

val matchRadius : int

val s1_l : int

val s2_l : int

val commonChars : (string -> string -> char list)

val chars1 : string

val chars2 : string

val matchChar : char

val windowChars : char list

Multiple items
module List

from Microsoft.FSharp.Collections

--------------------
type List<'T> =
  | ( [] )
  | ( :: ) of Head: 'T * Tail: 'T list
  interface IEnumerable
  interface IEnumerable<'T>
  member Head : 'T
  member IsEmpty : bool
  member Item : index:int -> 'T with get
  member Length : int
  member Tail : 'T list
  static member Cons : head:'T * tail:'T list -> 'T list
  static member Empty : 'T list

Full name: Microsoft.FSharp.Collections.List<_>

val exists : predicate:('T -> bool) -> list:'T list -> bool

Full name: Microsoft.FSharp.Collections.List.exists

val c : char

val common1 : char list

val common2 : char list

val totalTranspositions : float

val zip : list1:'T1 list -> list2:'T2 list -> ('T1 * 'T2) list

Full name: Microsoft.FSharp.Collections.List.zip

val fold : folder:('State -> 'T -> 'State) -> state:'State -> list:'T list -> 'State

Full name: Microsoft.FSharp.Collections.List.fold

val s : float

val c1 : char

val c2 : char

val transpositions : float

val s1length : float

Multiple items
val float : value:'T -> float (requires member op_Explicit)

Full name: Microsoft.FSharp.Core.Operators.float

--------------------
type float = System.Double

Full name: Microsoft.FSharp.Core.float

--------------------
type float<'Measure> = float

Full name: Microsoft.FSharp.Core.float<_>

val s2length : float

val c1length : float

val length : list:'T list -> int

Full name: Microsoft.FSharp.Collections.List.length

val c2length : float

val jaroWinkler : s1:string -> s2:string -> float

Full name: Script.jaroWinkler

val jaroScore : float

val p : float

val maxLength : int

property System.String.Length: int

val calcL : (int -> float -> float)

val acc : float

val l : float

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More information

Link:	http://fssnip.net/2M
Posted:	13 years ago
Author:	Rick Minerich
Tags:	text , matching