Calculate the similarity of two strings

similarity-of.red

Red [
    Title: "Similarity Of"
    Author: "Christopher Ross-Gill"
    Date: 25-Aug-2017
    File: %similarity-of.red
    Purpose: "Calculate the similarity (%) of two strings."
    Rights: http://opensource.org/licenses/Apache-2.0
]

do %simplediff.red
; from https://github.com/rgchris/Scripts/blob/master/red/simplediff.red

similarity-of: func [
    before [string!]
    after [string!]
][
    round 200% * (
        length? rejoin collect [
            foreach [disposition part] diff before after [
                if disposition = '= [keep part]
            ]
        ]
    ) / (
        add length? before length? after
    )
]

probe similarity-of "Pencilvaneya" "Pennsylvania"

Inspired by Pattern Matching: The Gestalt Approach.