Dice coefficient for string similarity on natural text

dicecoefficient.go

/* 
	Dice coefficient for string similarity on natural text
	Playground: http://play.golang.org/p/JFUjcpBb66
*/

package dicecoefficient

import "strings"
import "unicode"

func calculateSimilarity(str1, str2 string) float32 {
	if str1 == str2 {
		return 1.0
	}
	//get bigrams excluding whitespace
	pairs := func(str string) []bigram {
		runes := []rune(strings.ToLower(str))
		n := len(runes) - 1
		pairs := make([]bigram, n)
		e := 0
		for i := 0; i < n; i++ {
			if !unicode.IsSpace(runes[i]) && !unicode.IsSpace(runes[i+1]) {
				copy(pairs[e][:], runes[i:i+2])
				e++
			}
		}
		return pairs[0:e]
	}
	pairs1, pairs2 := pairs(str1), pairs(str2)
	i := 0
	for _, p1 := range pairs1 {
		for p2, _ := range pairs2 {
			if p1 == pairs2[p2] {
				i++
				//exclude already found pairs on the next run
				pairs2[p2] = bigram{}
				break
			}
		}
	}
	return (2.0 * float32(i)) / (float32(len(pairs1) + len (pairs2)))
}