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Calculate left margins

Take some text and work out where the left margins are, returning the most common margin settings first. Useful for processing somewhat messy text items like movie scripts. Left margins are defined by leading spaces. Tabs must be expanded before calling.

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let margins (lines : seq<string>) =
    let marginWidth (line : string) =
        line.Length - line.TrimStart([|' '|]).Length 
    lines
    |> Seq.map (fun line -> marginWidth line)
    |> Seq.countBy (fun width -> width)
    |> Seq.filter (fun margCount -> fst(margCount) > 0)
    |> Seq.sortBy (fun margCount -> -snd(margCount))

// Example:
let lines = [
                "This has no margin."
                " This has a one-space margin."
                " So does this."
                "      These three lines have a six-space margin."
                "      Again with the six-space margin."
                "      And again."
                " Back to one space."
                "      And finally, another six space."
            ]

// Output: seq [(6, 4); (1, 3)]
lines |> margins

val margins : lines:seq<string> -> seq<int * int>

Full name: Script.margins

val lines : seq<string>

Multiple items
val seq : sequence:seq<'T> -> seq<'T>

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

--------------------
type seq<'T> = System.Collections.Generic.IEnumerable<'T>

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

Multiple items
val string : value:'T -> string

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

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

Full name: Microsoft.FSharp.Core.string

val marginWidth : (string -> int)

val line : string

property System.String.Length: int

System.String.TrimStart([<System.ParamArray>] trimChars: char []) : string

module Seq

from Microsoft.FSharp.Collections

val map : mapping:('T -> 'U) -> source:seq<'T> -> seq<'U>

Full name: Microsoft.FSharp.Collections.Seq.map

val countBy : projection:('T -> 'Key) -> source:seq<'T> -> seq<'Key * int> (requires equality)

Full name: Microsoft.FSharp.Collections.Seq.countBy

val width : int

val filter : predicate:('T -> bool) -> source:seq<'T> -> seq<'T>

Full name: Microsoft.FSharp.Collections.Seq.filter

val margCount : int * int

val fst : tuple:('T1 * 'T2) -> 'T1

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

val sortBy : projection:('T -> 'Key) -> source:seq<'T> -> seq<'T> (requires comparison)

Full name: Microsoft.FSharp.Collections.Seq.sortBy

val snd : tuple:('T1 * 'T2) -> 'T2

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

val lines : string list

Full name: Script.lines

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More information

Link:	http://fssnip.net/9K
Posted:	12 years ago
Author:	Kit Eason
Tags:	margins text