similarity.go

/*
 * Simple recommendation engine
 *     Copyright (c) 2014, Christian Muehlhaeuser <muesli@gmail.com>
 *
 *   For license see LICENSE.txt
 */

package regommend

import (
	_ "errors"
	_ "log"
	_ "fmt"
	"math"
)

func cosineSim(t1, t2 map[interface{}]float64) float64 {
	sum_xy := 0.0
	sum_x2 := 0.0
	sum_y2 := 0.0

	for key, x := range t1 {
		y, _ := t2[key]
		{
//			fmt.Println("Found shared:", key, x, y)

			sum_xy += x * y
			sum_x2 += math.Pow(x, 2)
			sum_y2 += math.Pow(y, 2)
		}
	}

	denominator := math.Sqrt(sum_x2) * math.Sqrt(sum_y2)
	if denominator == 0 {
		return 0
	}

	return sum_xy / denominator
}

func pearsonSim(t1, t2 map[interface{}]float64) float64 {
	sum_xy := 0.0
	sum_x := 0.0
	sum_y := 0.0
	sum_x2 := 0.0
	sum_y2 := 0.0
	n := 0.0

	for key, x := range t1 {
		y, ok := t2[key]
		if ok {
//			fmt.Println("Found shared:", key, x, y)
			n++

			sum_xy += x * y
			sum_x += x
			sum_y += y
			sum_x2 += math.Pow(x, 2)
			sum_y2 += math.Pow(y, 2)
		}
	}

	if n == 0 {
		// no common items found
		return 0
	}

	denominator := (math.Sqrt(sum_x2 - math.Pow(sum_x, 2) / n) *
					math.Sqrt(sum_y2 - math.Pow(sum_y, 2) / n))
	if denominator == 0 {
		return 0
	}

	return (sum_xy - (sum_x * sum_y) / n) / denominator
}