From 61793326a3311ed3c58541dc61eeec3b1d972bbe Mon Sep 17 00:00:00 2001
From: Gea-Suan Lin <gslin@gslin.org>
Date: Wed, 28 Feb 2024 06:16:56 +0800
Subject: [PATCH] Implement BM25 version.

---
 cmd/ir-bm25/main.go | 65 +++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 65 insertions(+)

diff --git a/cmd/ir-bm25/main.go b/cmd/ir-bm25/main.go
index da29a2c..37f3e35 100644
--- a/cmd/ir-bm25/main.go
+++ b/cmd/ir-bm25/main.go
@@ -1,4 +1,69 @@
 package main
 
+import (
+	"fmt"
+	"math"
+	"os"
+	"strings"
+
+	"github.com/gslin/go-ir-playground/internal/artifact"
+	"github.com/gslin/go-ir-playground/internal/tokenizer"
+)
+
 func main() {
+	if len(os.Args) < 2 {
+		fmt.Printf("You need to specify a keyword to search.\n")
+		os.Exit(1)
+	}
+
+	articles := artifact.Read("data/articles.json")
+
+	tokens := make(map[string][]string)
+	token_num := 0
+	tf := make(map[string]map[string]int)
+	df := make(map[string]int)
+
+	for _, article := range articles {
+		id := article.Id
+		str := strings.ToLower(article.Title + "\n" + article.Body)
+
+		bag := tokenizer.Tokenize(str)
+		tokens[id] = bag
+
+		token_num += len(bag)
+
+		for _, w := range bag {
+			// Handle TF:
+			if _, ok := tf[w]; !ok {
+				tf[w] = make(map[string]int)
+			}
+			tf[w][id] += strings.Count(str, w)
+
+			// Handle DF:
+			df[w] += 1
+		}
+	}
+
+	fmt.Println("TF & DF Built")
+
+	n := len(articles)
+	avgdl := float64(token_num / n)
+	q := strings.ToLower(os.Args[1])
+	q_tokens := tokenizer.Tokenize(q)
+
+	for _, article := range articles {
+		id := article.Id
+
+		var score float64 = 0.0
+		for _, w := range q_tokens {
+			if tf[w] != nil {
+				idf := math.Log2((float64(n - df[w]) + 0.5) / (float64(df[w]) + 0.5) + 1)
+				score += idf * (float64(tf[w][id]) * 2.2) / (float64(tf[w][id]) + 1.2 * (0.25 + 0.75 * (float64(n) / avgdl)))
+			}
+		}
+
+		if score > 0 {
+			fmt.Printf("Article %v (https://blog.gslin.org/?p=%v): %v\n", id, id, score)
+		}
+	}
 }