recommender systems

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  1. 1. Gordon Lesti Recommender Systems Student @GordonLesti gordonlesti.com
  2. 2. Typical problems
  3. 3. Typical problems What other items do customer buy after viewing this item
  4. 4. Typical problems What other items do customer buy after viewing this item Who to follow
  5. 5. Typical problems What other items do customer buy after viewing this item Who to follow People who viewed this item also viewed
  6. 6. Typical problems What other items do customer buy after viewing this item Who to follow People who viewed this item also viewed Related or similar movies?
  7. 7. Typical problems What other items do customer buy after viewing this item Who to follow People who viewed this item also viewed Related or similar movies? . . .
  8. 8. Basic concepts
  9. 9. Basic concepts Collaborative recommendation
  10. 10. Basic concepts Collaborative recommendation Content-based recommendation
  11. 11. Basic concepts Collaborative recommendation Content-based recommendation Knowledge-based recommendation
  12. 12. Basic concepts Collaborative recommendation Content-based recommendation Knowledge-based recommendation Hybrid recommendation
  13. 13. Compare items Item1 1 2 5 3 , Item2 4 3 4 1 , Item3 2 1 4 5
  14. 14. Cosine similarity measure sim(a , b ) = a b |a || b |
  15. 15. sim(Item1, Item2) = 14+23+54+31 12+22+52+32 42+32+42+12 0.81537424832721117
  16. 16. sim(Item1, Item2) = 14+23+54+31 12+22+52+32 42+32+42+12 0.81537424832721117 sim(Item1, Item3) = 12+21+54+35 12+22+52+32 22+12+42+52 0.92077472106727698
  17. 17. sim(Item1, Item2) = 14+23+54+31 12+22+52+32 42+32+42+12 0.81537424832721117 sim(Item1, Item3) = 12+21+54+35 12+22+52+32 22+12+42+52 0.92077472106727698 sim(Item1, Item3) = 42+31+44+15 42+32+42+12 22+12+42+52 0.72802520830926409
  18. 18. Item1 Item2 Item3 Item1 1.0 0.815 0.921 Item2 0.815 1.0 0.728 Item3 0.921 0.728 1.0
  19. 19. Conventions U = {u1, . . . , un} set of users P = {p1, . . . , pm} set of products (items) R is a n m matrix of ratings ri,j with i 1 . . . n, j 1 . . . m