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[rewards] use dense rep penalty #296

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[rewards] use dense rep penalty #296

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a82e554
use dense rep penalty
kashif Feb 12, 2025
473cad8
formatting
kashif Feb 12, 2025
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40 changes: 26 additions & 14 deletions src/open_r1/rewards.py
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Original file line number Diff line number Diff line change
Expand Up @@ -150,7 +150,7 @@ def cosine_scaled_reward(completions, solution, **kwargs):
return cosine_scaled_reward


def get_repetition_penalty_reward(ngram_size: int, max_penalty: float):
def get_repetition_penalty_reward(ngram_size: int, max_penalty: float, only_start: bool = False):
"""
Computes N-gram repetition penalty as described in Appendix C.2 of https://arxiv.org/abs/2502.03373.
Reference implementation from: https://github.com/eddycmu/demystify-long-cot/blob/release/openrlhf/openrlhf/reward/repetition.py
Expand All @@ -162,9 +162,8 @@ def get_repetition_penalty_reward(ngram_size: int, max_penalty: float):
if max_penalty > 0:
raise ValueError(f"max_penalty {max_penalty} should not be positive")

def zipngram(text: str, ngram_size: int):
words = text.lower().split()
return zip(*[words[i:] for i in range(ngram_size)])
def zipngram(tokens: list[str], ngram_size: int):
return zip(*[tokens[i:] for i in range(ngram_size)])

def repetition_penalty_reward(completions, **kwargs) -> float:
"""
Expand All @@ -178,22 +177,35 @@ def repetition_penalty_reward(completions, **kwargs) -> float:
contents = [completion[0]["content"] for completion in completions]
rewards = []
for completion in contents:
if completion == "":
rewards.append(0.0)
continue
if len(completion.split()) < ngram_size:
if completion == "" or len(completion.split()) < ngram_size:
rewards.append(0.0)
continue

# Find repeated n-grams and their positions
words = completion.lower().split()
repeated_positions = []
ngrams = set()
total = 0
for ng in zipngram(completion, ngram_size):

for start_idx, ng in enumerate(zipngram(words, ngram_size)):
if ng in ngrams:
repeated_positions.append(start_idx)
ngrams.add(ng)
total += 1

scaling = 1 - len(ngrams) / total
reward = scaling * max_penalty
rewards.append(reward)
# Calculate word-level penalties
word_penalties = [0.0] * len(words)
curr_end_idx = -1

for start_idx in repeated_positions:
if not only_start or start_idx > curr_end_idx:
# Apply penalty to each token in the repeated n-gram
for i in range(start_idx, start_idx + ngram_size):
word_penalties[i] = max_penalty
curr_end_idx = start_idx + ngram_size

# Average the word-level penalties for the final reward
reward = sum(word_penalties) / len(word_penalties) if word_penalties else 0.0
rewards.append(float(reward))

return rewards

return repetition_penalty_reward
14 changes: 7 additions & 7 deletions tests/test_rewards.py
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Original file line number Diff line number Diff line change
Expand Up @@ -130,7 +130,7 @@ def test_full_repetition(self):

rewards = reward_fn(completions)
# (1 - 1/4) * -1 = -0.75
self.assertEqual(rewards, [-0.75])
self.assertEqual(rewards, [-0.8])

def test_partial_repetition(self):
reward_fn = get_repetition_penalty_reward(ngram_size=2, max_penalty=-1.0)
Expand All @@ -139,7 +139,7 @@ def test_partial_repetition(self):
rewards = reward_fn(completions)
# Unique 2-grams: (this, is), (is, a), (a, this), (a, test). 4 unique out of 6 total
# (1 - 4/6) * -1 = -1/3 = -0.3333...
self.assertAlmostEqual(rewards[0], -1 / 3)
self.assertAlmostEqual(rewards[0], -0.4285714, places=4)

def test_multiple_completions(self):
reward_fn = get_repetition_penalty_reward(ngram_size=3, max_penalty=-0.5)
Expand All @@ -152,7 +152,7 @@ def test_multiple_completions(self):
# Completion 1: (this, is, a), (is, a, test) -> 2 unique / 2 total -> (1 - 2/2) * -0.5 = 0
# Completion 2: (test, test, test) -> 1 unique / 2 total -> (1 - 1/2) * -0.5 = -0.25
self.assertAlmostEqual(rewards[0], 0.0)
self.assertAlmostEqual(rewards[1], -0.25)
self.assertAlmostEqual(rewards[1], -0.375)

def test_empty_completion(self):
reward_fn = get_repetition_penalty_reward(ngram_size=2, max_penalty=-1.0)
Expand All @@ -165,7 +165,7 @@ def test_different_ngram_size(self):
completions = [[{"content": "this is a this is a test"}]]

rewards = reward_fn(completions)
self.assertAlmostEqual(rewards[0], -0.4)
self.assertAlmostEqual(rewards[0], -0.8571428, places=4)

def test_mixed_case(self):
reward_fn = get_repetition_penalty_reward(ngram_size=2, max_penalty=-1.0)
Expand Down Expand Up @@ -204,7 +204,7 @@ def test_three_word_repetition_completion(self):
completions = [[{"content": "word word word word"}]]

rewards = reward_fn(completions)
self.assertEqual(rewards, [-0.5])
self.assertEqual(rewards, [-0.75])

def test_four_word_completion_with_repetition(self):
reward_fn = get_repetition_penalty_reward(ngram_size=3, max_penalty=-1.0)
Expand All @@ -227,13 +227,13 @@ def test_six_word_completion_with_repetition(self):
completions = [[{"content": "A B C A B C"}]]

rewards = reward_fn(completions)
self.assertEqual(rewards, [-0.25])
self.assertEqual(rewards, [-0.5])

def test_long_completion_with_repetition(self):
reward_fn = get_repetition_penalty_reward(ngram_size=3, max_penalty=-1.0)
completions = [[{"content": "A B C A B C E F G A B C A B C"}]]
rewards = reward_fn(completions)
self.assertAlmostEqual(rewards[0], -0.3846, places=4)
self.assertAlmostEqual(rewards[0], -0.6)

def test_long_completion_without_repetition(self):
reward_fn = get_repetition_penalty_reward(ngram_size=3, max_penalty=-1.0)
Expand Down