Changes between Version 5 and Version 6 of tutorial/ProbabilisticLearningModels
- Timestamp:
- 08/14/09 09:40:47 (15 years ago)
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tutorial/ProbabilisticLearningModels
v5 v6 32 32 Feature extraction is the task of extracting features from examples. 33 33 {{{ 34 E.g., In our document classification scenario, a tokenizer that extracts words from text might be used for feature extraction. 34 E.g., In our document classification scenario, a tokenizer that extracts words from 35 text might be used for feature extraction. 35 36 }}} 36 37 In more sophisticated scenarios, feature extraction can be hierarchically nested by extracting new features from existing feature lists. 37 38 {{{ 38 E.g., In our document classification scenario, a word n-gram algorithm extracts n-gram features from extracted word sequences. 39 E.g., In our document classification scenario, a word n-gram algorithm extracts n-gram 40 features from extracted word sequences. 39 41 }}} 40 42 … … 44 46 First, not all features are useful for separating different classes. In details, there is no statistically significant dependency between class and feature occurance. 45 47 {{{ 46 E.g., In our document classification scenario, stop words or high frequent words are not useful for separating e.g., spam mails from ham mails. 48 E.g., In our document classification scenario, stop words or high frequent words are 49 not useful for separating e.g., spam mails from ham mails. 47 50 }}} 48 51 Second, just a small set of features might be enough for classifiying examples successfully. Adding more just decreases performance.