文本相似度计算（TF-IDF）C#

namespace ServiceRanking { /// <summary> /// Summary description for TF_IDFLib. /// </summary> public class TFIDFMeasure { private string[] _docs; private string[][] _ngramDoc; private int _numDocs=0; private int _numTerms=0; private ArrayList _terms; private int[][] _termFreq; private float[][] _termWeight; private int[] _maxTermFreq; private int[] _docFreq; public class TermVector { public static float ComputeCosineSimilarity(float[] vector1, float[] vector2) { if (vector1.Length != vector2.Length) throw new Exception("DIFER LENGTH"); float denom=(VectorLength(vector1) * VectorLength(vector2)); if (denom == 0F) return 0F; else return (InnerProduct(vector1, vector2) / denom); } public static float InnerProduct(float[] vector1, float[] vector2) { if (vector1.Length != vector2.Length) throw new Exception("DIFFER LENGTH ARE NOT ALLOWED"); float result=0F; for (int i=0; i < vector1.Length; i++) result += vector1[i] * vector2[i]; return result; } public static float VectorLength(float[] vector) { float sum=0.0F; for (int i=0; i < vector.Length; i++) sum=sum + (vector[i] * vector[i]); return (float)Math.Sqrt(sum); } } private IDictionary _wordsIndex=new Hashtable() ; public TFIDFMeasure(string[] documents) { _docs=documents; _numDocs=documents.Length ; MyInit(); } private void GeneratNgramText() { } private ArrayList GenerateTerms(string[] docs) { ArrayList uniques=new ArrayList() ; _ngramDoc=new string[_numDocs][] ; for (int i=0; i < docs.Length ; i++) { Tokeniser tokenizer=new Tokeniser() ; string[] words=tokenizer.Partition(docs[i]); for (int j=0; j < words.Length ; j++) if (!uniques.Contains(words[j]) ) uniques.Add(words[j]) ; } return uniques; } private static object AddElement(IDictionary collection, object key, object newValue) { object element=collection[key]; collection[key]=newValue; return element; } private int GetTermIndex(string term) { object index=_wordsIndex[term]; if (index == null) return -1; return (int) index; } private void MyInit() { _terms=GenerateTerms (_docs ); _numTerms=_terms.Count ; _maxTermFreq=new int[_numDocs] ; _docFreq=new int[_numTerms] ; _termFreq =new int[_numTerms][] ; _termWeight=new float[_numTerms][] ; for(int i=0; i < _terms.Count ; i++) { _termWeight[i]=new float[_numDocs] ; _termFreq[i]=new int[_numDocs] ; AddElement(_wordsIndex, _terms[i], i); } GenerateTermFrequency (); GenerateTermWeight(); } private float Log(float num) { return (float) Math.Log(num) ;//log2 } private void GenerateTermFrequency() { for(int i=0; i < _numDocs ; i++) { string curDoc=_docs[i]; IDictionary freq=GetWordFrequency(curDoc); IDictionaryEnumerator enums=freq.GetEnumerator() ; _maxTermFreq[i]=int.MinValue ; while (enums.MoveNext()) { string word=(string)enums.Key; int wordFreq=(int)enums.Value ; int termIndex=GetTermIndex(word); _termFreq [termIndex][i]=wordFreq; _docFreq[termIndex] ++; if (wordFreq > _maxTermFreq[i]) _maxTermFreq[i]=wordFreq; } } } private void GenerateTermWeight() { for(int i=0; i < _numTerms ; i++) { for(int j=0; j < _numDocs ; j++) _termWeight[i][j]=ComputeTermWeight (i, j); } } private float GetTermFrequency(int term, int doc) { int freq=_termFreq [term][doc]; int maxfreq=_maxTermFreq[doc]; return ( (float) freq/(float)maxfreq ); } private float GetInverseDocumentFrequency(int term) { int df=_docFreq[term]; return Log((float) (_numDocs) / (float) df ); } private float ComputeTermWeight(int term, int doc) { float tf=GetTermFrequency (term, doc); float idf=GetInverseDocumentFrequency(term); return tf * idf; } private float[] GetTermVector(int doc) { float[] w=new float[_numTerms] ; for (int i=0; i < _numTerms; i++) w[i]=_termWeight[i][doc]; return w; } public float GetSimilarity(int doc_i, int doc_j) { float[] vector1=GetTermVector (doc_i); float[] vector2=GetTermVector (doc_j); return TermVector.ComputeCosineSimilarity(vector1, vector2) ; } private IDictionary GetWordFrequency(string input) { string convertedInput=input.ToLower() ; Tokeniser tokenizer=new Tokeniser() ; String[] words=tokenizer.Partition(convertedInput); Array.Sort(words); String[] distinctWords=GetDistinctWords(words); IDictionary result=new Hashtable(); for (int i=0; i < distinctWords.Length; i++) { object tmp; tmp=CountWords(distinctWords[i], words); result[distinctWords[i]]=tmp; } return result; } private string[] GetDistinctWords(String[] input) { if (input == null) return new string[0]; else { ArrayList list=new ArrayList() ; for (int i=0; i < input.Length; i++) if (!list.Contains(input[i])) // N-GRAM SIMILARITY? list.Add(input[i]); return Tokeniser.ArrayListToArray(list) ; } } private int CountWords(string word, string[] words) { int itemIdx=Array.BinarySearch(words, word); if (itemIdx > 0) while (itemIdx > 0 && words[itemIdx].Equals(word)) itemIdx--; int count=0; while (itemIdx < words.Length && itemIdx >= 0) { if (words[itemIdx].Equals(word)) count++; itemIdx++; if (itemIdx < words.Length) if (!words[itemIdx].Equals(word)) break; } return count; } } }