From b309263df5b2655221e3f6416813f3da8bea11c1 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?=E3=81=BF=E3=81=A6=E3=82=8B=E3=81=9E?= <miteruzo@naver.com>
Date: Wed, 7 Jan 2026 03:25:27 +0900
Subject: [PATCH] =?UTF-8?q?feat:=20=E9=96=A2=E8=81=AF=E3=82=BF=E3=82=B0?=
 =?UTF-8?q?=EF=BC=88#92=EF=BC=89=20(#197)?=
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Merge branch 'main' into #92

Merge remote-tracking branch 'origin/main' into #92

#92

Co-authored-by: miteruzo <miteruzo@naver.com>
Reviewed-on: https://git.miteruzo.com/miteruzo/btrc-hub/pulls/197
---
 backend/app/models/tag_similarity.rb         |  4 +++
 backend/lib/tasks/calc_tag_similarities.rake | 28 ++++++++++++++++++++
 2 files changed, 32 insertions(+)
 create mode 100644 backend/app/models/tag_similarity.rb
 create mode 100644 backend/lib/tasks/calc_tag_similarities.rake

diff --git a/backend/app/models/tag_similarity.rb b/backend/app/models/tag_similarity.rb
new file mode 100644
index 0000000..d983409
--- /dev/null
+++ b/backend/app/models/tag_similarity.rb
@@ -0,0 +1,4 @@
+class TagSimilarity < ApplicationRecord
+  belongs_to :tag, class_name: 'Tag', foreign_key: 'tag_id'
+  belongs_to :target_tag, class_name: 'Tag', foreign_key: 'target_tag_id'
+end
diff --git a/backend/lib/tasks/calc_tag_similarities.rake b/backend/lib/tasks/calc_tag_similarities.rake
new file mode 100644
index 0000000..9e16977
--- /dev/null
+++ b/backend/lib/tasks/calc_tag_similarities.rake
@@ -0,0 +1,28 @@
+namespace :tag_similarity do
+  desc '関聯タグ・テーブル作成'
+  task calc: :environment do
+    dot = -> a, b { (a.keys & b.keys).sum { |k| a[k] * b[k] } }
+    norm = -> v { Math.sqrt(v.values.sum { |e| e * e }) }
+    cos = -> a, b do
+      na = norm.(a)
+      nb = norm.(b)
+      if na.zero? || nb.zero?
+        0.0
+      else
+        dot.(a, b) / na / nb
+      end
+    end
+
+    tags = Tag.includes(:posts).to_a
+    tags.each_with_index do |tag, i|
+      existence_of_posts = tag.posts.index_with(1)
+      ((i + 1)...tags.size).each do |j|
+        target_tag = tags[j]
+        existence_of_target_posts = target_tag.posts.index_with(1)
+        TagSimilarity.find_or_initialize_by(tag:, target_tag:).tap { |ts|
+          ts.cos = cos.(existence_of_posts, existence_of_target_posts)
+        }.save!
+      end
+    end
+  end
+end