2 people like it.

Similar string Markov chain

Generates strings that are similar to the input, as measured by the probability of a symbol depending on preceding symbols. (Markov chain) The order, which defines how many preceding symbols to look at before placing another, is variable.

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// Generates strings that are similar to the input, as measured by the
// probability of a symbol depending on preceding symbols. (Markov chain)
// The order defines how many preceding symbols to look at to place another.

/// Reads a map of next characters' probabilities from a sample.
let readMap order (s : string) =
    s |> Seq.windowed (order + 1)
    |> Seq.groupBy (fun a -> System.String( a.[0..order - 1] ))
    |> Seq.map (fun (a, b) ->
        let counted = b |> Seq.map (fun arr -> arr.[order])
                        |> Seq.countBy id |> Seq.toList
        let total = List.sumBy snd counted
        a, counted |> List.map (fun (c, i) -> c, float i / float total))
    |> Map.ofSeq

// System.Random is broken. Replace it if you want reliable randomness.
let random = let r = System.Random() in fun () -> r.NextDouble()

/// Helper to get one character from a list of choices with probabilities
let getChar prev cases =
    let rec run r = function
        | [] -> failwith "getChar error"
        | (c, p) :: t when r > p -> run (r-p) t
        | (c, _) :: _ -> c
    run (random() * 0.999) cases // precision safety

/// Creates text according to a distribution. Fills in spaces if accumulator is empty.
let rec generate order length acc map =
    if length < 1 then acc else
    let acc' =
        if String.length acc < order then sprintf "%s " acc else
        let sub = acc.Substring(acc.Length - order)
        if Map.containsKey sub map then sprintf "%s%c" acc (getChar sub map.[sub])
        else failwith (sprintf "No viable solution in map for %s." sub)
    generate order (length - 1) acc' map

/// Generates words from sample. Generates space-separated words independently.
let wordwise order approxLength input =
    let out = (" " + input + " ").Replace(" ", String.replicate order " ")
              |> readMap order |> generate order approxLength ""
    out.Replace(String.replicate order " ", " ").Remove(0,1) |> printfn "%s"


// Samples (input a long list of names to get more useful results):

let lolz = "lololololol zomg roflmao"
wordwise 1 60 lolz
wordwise 2 60 lolz

"Mercury Venus Earth Mars Asteroid Belt Jupiter Saturn Neptune Pluto Moon Terra Luna \
Adrastea Ganymede Callisto Europa Himalia Amalthea Thebe Elara Metis Pasiphae Carme \
Sinope Lysithea Ananke Leda Themisto Callirrhoe Praxidike Megaclite Locaste Taygete \
Kalyke Autonoe Harpalyke Titan Rhea Iapetus Dione Tethys Enceladus Mimas Hyperion \
Phoebe Janus Epimetheus Prometheus Pandora Titania Oberon Umbriel Ariel Miranda \
Sycorax Puck Portia Juliet Caliban Belinda Cressida Triton Proteus Nereid Larissa \
Galatea Despina Thalassa Charon"
|> wordwise 2 200
val readMap : order:int -> s:string -> Map<System.String,(char * float) list>

Full name: Script.readMap


 Reads a map of next characters' probabilities from a sample.
val order : int
val s : string
Multiple items
val string : value:'T -> string

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

--------------------
type string = System.String

Full name: Microsoft.FSharp.Core.string
module Seq

from Microsoft.FSharp.Collections
val windowed : windowSize:int -> source:seq<'T> -> seq<'T []>

Full name: Microsoft.FSharp.Collections.Seq.windowed
val groupBy : projection:('T -> 'Key) -> source:seq<'T> -> seq<'Key * seq<'T>> (requires equality)

Full name: Microsoft.FSharp.Collections.Seq.groupBy
val a : char []
namespace System
Multiple items
type String =
  new : value:char -> string + 7 overloads
  member Chars : int -> char
  member Clone : unit -> obj
  member CompareTo : value:obj -> int + 1 overload
  member Contains : value:string -> bool
  member CopyTo : sourceIndex:int * destination:char[] * destinationIndex:int * count:int -> unit
  member EndsWith : value:string -> bool + 2 overloads
  member Equals : obj:obj -> bool + 2 overloads
  member GetEnumerator : unit -> CharEnumerator
  member GetHashCode : unit -> int
  ...

Full name: System.String

--------------------
System.String(value: nativeptr<char>) : unit
System.String(value: nativeptr<sbyte>) : unit
System.String(value: char []) : unit
System.String(c: char, count: int) : unit
System.String(value: nativeptr<char>, startIndex: int, length: int) : unit
System.String(value: nativeptr<sbyte>, startIndex: int, length: int) : unit
System.String(value: char [], startIndex: int, length: int) : unit
System.String(value: nativeptr<sbyte>, startIndex: int, length: int, enc: System.Text.Encoding) : unit
val map : mapping:('T -> 'U) -> source:seq<'T> -> seq<'U>

Full name: Microsoft.FSharp.Collections.Seq.map
val a : System.String
val b : seq<char []>
val counted : (char * int) list
val arr : char []
val countBy : projection:('T -> 'Key) -> source:seq<'T> -> seq<'Key * int> (requires equality)

Full name: Microsoft.FSharp.Collections.Seq.countBy
val id : x:'T -> 'T

Full name: Microsoft.FSharp.Core.Operators.id
val toList : source:seq<'T> -> 'T list

Full name: Microsoft.FSharp.Collections.Seq.toList
val total : int
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 sumBy : projection:('T -> 'U) -> list:'T list -> 'U (requires member ( + ) and member get_Zero)

Full name: Microsoft.FSharp.Collections.List.sumBy
val snd : tuple:('T1 * 'T2) -> 'T2

Full name: Microsoft.FSharp.Core.Operators.snd
val map : mapping:('T -> 'U) -> list:'T list -> 'U list

Full name: Microsoft.FSharp.Collections.List.map
val c : char
val i : int
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<_>
Multiple items
module Map

from Microsoft.FSharp.Collections

--------------------
type Map<'Key,'Value (requires comparison)> =
  interface IEnumerable
  interface IComparable
  interface IEnumerable<KeyValuePair<'Key,'Value>>
  interface ICollection<KeyValuePair<'Key,'Value>>
  interface IDictionary<'Key,'Value>
  new : elements:seq<'Key * 'Value> -> Map<'Key,'Value>
  member Add : key:'Key * value:'Value -> Map<'Key,'Value>
  member ContainsKey : key:'Key -> bool
  override Equals : obj -> bool
  member Remove : key:'Key -> Map<'Key,'Value>
  ...

Full name: Microsoft.FSharp.Collections.Map<_,_>

--------------------
new : elements:seq<'Key * 'Value> -> Map<'Key,'Value>
val ofSeq : elements:seq<'Key * 'T> -> Map<'Key,'T> (requires comparison)

Full name: Microsoft.FSharp.Collections.Map.ofSeq
val random : (unit -> float)

Full name: Script.random
val r : System.Random
Multiple items
type Random =
  new : unit -> Random + 1 overload
  member Next : unit -> int + 2 overloads
  member NextBytes : buffer:byte[] -> unit
  member NextDouble : unit -> float

Full name: System.Random

--------------------
System.Random() : unit
System.Random(Seed: int) : unit
System.Random.NextDouble() : float
val getChar : prev:'a -> cases:('b * float) list -> 'b

Full name: Script.getChar


 Helper to get one character from a list of choices with probabilities
val prev : 'a
val cases : ('b * float) list
val run : (float -> ('c * float) list -> 'c)
val r : float
val failwith : message:string -> 'T

Full name: Microsoft.FSharp.Core.Operators.failwith
val c : 'c
val p : float
val t : ('c * float) list
val generate : order:int -> length:int -> acc:string -> map:Map<string,(char * float) list> -> string

Full name: Script.generate


 Creates text according to a distribution. Fills in spaces if accumulator is empty.
val length : int
val acc : string
val map : Map<string,(char * float) list>
val acc' : string
module String

from Microsoft.FSharp.Core
val length : str:string -> int

Full name: Microsoft.FSharp.Core.String.length
val sprintf : format:Printf.StringFormat<'T> -> 'T

Full name: Microsoft.FSharp.Core.ExtraTopLevelOperators.sprintf
val sub : string
System.String.Substring(startIndex: int) : string
System.String.Substring(startIndex: int, length: int) : string
property System.String.Length: int
val containsKey : key:'Key -> table:Map<'Key,'T> -> bool (requires comparison)

Full name: Microsoft.FSharp.Collections.Map.containsKey
val wordwise : order:int -> approxLength:int -> input:string -> unit

Full name: Script.wordwise


 Generates words from sample. Generates space-separated words independently.
val approxLength : int
val input : string
val out : string
val replicate : count:int -> str:string -> string

Full name: Microsoft.FSharp.Core.String.replicate
System.String.Replace(oldValue: string, newValue: string) : string
System.String.Replace(oldChar: char, newChar: char) : string
val printfn : format:Printf.TextWriterFormat<'T> -> 'T

Full name: Microsoft.FSharp.Core.ExtraTopLevelOperators.printfn
val lolz : string

Full name: Script.lolz

More information

Link:http://fssnip.net/ol
Posted:3 years ago
Author:Vandroiy
Tags: random , generator , markov chain

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