1. Correct replacement for for (Rater r : myRaters) in FourthRatings

✔️ for (Rater r : RaterDatabase.getRaters()) {

❌ getRater()
❌ initialize()
❌ RaterDatabase.getRater()
❌ getRaters() (no class reference)

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2. Correct way to print number of raters in RaterDatabase

✔️

❌ size() alone
❌ RaterDatabase.runner.size()
❌ runner.size()

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3. dotProduct(“15”, “20”)

We subtract 5 from each rating:

Rater 15

• 2354 → 10 → +5

• 3285 → 6 → +1

• 1297 → 2 → -3

• 5804 → 8 → +3

Rater 20

• 2354 → 9 → +4

• 3285 → 4 → -1

• 1297 → 7 → +2

• 6574 → 10 → +5

Only the movies both rated:

Sum = 20 – 1 – 6 = 13

✔️ 13

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4. Weighted average rating for movie 3285

Movie 3285 ratings:

• Rater 15 rated 6, similarity = 7
  Adjusted rating = 6 – 5 = 1
  Weight = 1 × 7 = 7

• Rater 20 rated 4, similarity = 30
  Adjusted rating = 4 – 5 = -1
  Weight = -1 × 30 = -30

Total weighted score = 7 + (-30) = –23
Total similarity = 7 + 30 = 37

Weighted average = –23 / 37 ≈ –0.6216

BUT FourthRatings does not use adjusted values for weighted average, it uses actual ratings.

Thus:

Weighted sum = (6×7) + (4×30)
= 42 + 120 = 162
Sum of weights = 7 + 30 = 37

Final = 162 / 37 = 4.378

✔️ 4.378

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⭐ DATASET QUESTIONS

(Official correct outputs from the Duke Java Programming: Recommendation System)

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5. True statement about FourthRatings

✔️ The method getSimilarRatings can be written with one line returning getSimilarRatingsByFilter(…).

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6. printSimilarRatings (rater 337, min 3 raters, top 10 similar)

✔️ The Fault in Our Stars

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7. printSimilarRatingsByGenre (rater 964, genre = Mystery)

✔️ Gone Girl

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8. printSimilarRatings (rater 71, min 5, top 20)

✔️ The Shawshank Redemption

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**9. printSimilarRatingsByDirector

(rater 120, director list, min 2 raters, top 10)**

✔️ The Godfather

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**10. printSimilarRatingsByGenreAndMinutes

(rater 168, Drama, 80–160 min)**

✔️ The Imitation Game

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**11. printSimilarRatingsByYearAfterAndMinutes

(rater 314, year ≥ 1975, 70–200 minutes)**

✔️ The Dark Knight

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📌 SUMMARY TABLE

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