#59

backend/lib/tasks/calc_post_similarities.rake

@@ -0,0 +1,28 @@
+namespace :post_similarity do
+  desc '関聯投稿テーブル作成'
+  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
+
+    posts = Post.includes(:tags).to_a
+    posts.each_with_index do |post, i|
+      existence_of_tags = post.tags.index_with(1)
+      ((i + 1)...posts.size).each do |j|
+        target_post = posts[j]
+        existence_of_target_tags = target_post.tags.index_with(1)
+        PostSimilarity.find_or_initialize_by(post:, target_post:).tap { |ps|
+          ps.cos = cos.(existence_of_tags, existence_of_target_tags)
+        }.save!
+      end
+    end
+  end
+end