³ò 3ÒÇIc@s‰dZddkZddklZddklZddkl Z ddk l Z l Z l Z ddkTdefd „ƒYZd efd „ƒYZd efd „ƒYZddd„Ze ƒZe ƒZedjo›ddkZddk l Z yedeidƒZWnej o dZnXyedeidƒZWnej o dZnXeeeƒnd d ddgZdS(sì Tools to identify X{collocation}s --- words that often appear consecutively --- within corpora. They may also be used to find other X{association}s between word occurrences. See Manning and Schutze ch. 5 at http://nlp.stanford.edu/fsnlp/promo/colloc.pdf and the Text::NSP Perl package at http://ngram.sourceforge.net Finding collocations requires first calculating the frequencies of words and their appearance in the context of other words. Often the collection of words will then requiring filtering to only retain useful content terms. Each ngram of words may then be scored according to some X{association measure}, in order to determine the relative likelihood of each ngram being a collocation. The L{BigramCollocationFinder} and L{TrigramCollocationFinder} classes provide these functionalities, dependent on being provided a function which scores a ngram given appropriate frequency counts. A number of standard association measures are provided in L{bigram_measures} and L{trigram_measures}. iÿÿÿÿN(t itemgetter(tFreqDist(tingrams(tContingencyMeasurestBigramAssocMeasurestTrigramAssocMeasures(t*tAbstractCollocationFindercBsƒeZdZd„Zed„ƒZed„ƒZd„d„Zd„Z d„Z d„Z d „Z d „Z d „Zd „ZRS( s” An abstract base class for X{collocation finder}s whose purpose is to collect collocation candidate frequencies, filter and rank them. cCs||_||_dS(sAs a minimum, collocation finders require the frequencies of each word in a corpus, and the joint frequency of word tuples. This data should be provided through L{nltk.probability.FreqDist} objects or an identical interface. N(tword_fdtngram_fd(tselfRR ((s'/p/zhu/06/nlp/nltk/nltk/collocations.pyt__init__0s cCs|iti|ŒƒS(s‚Constructs a collocation finder given a collection of documents, each of which is a list (or iterable) of tokens. (t from_wordst _itertoolstchain(tclst documents((s'/p/zhu/06/nlp/nltk/nltk/collocations.pytfrom_documents9scs-t‡‡fd†ttˆƒdƒDƒƒS(Nc3s*x#|]}tˆ||ˆ!ƒVqWdS(N(ttuple(t.0ti(tntwords(s'/p/zhu/06/nlp/nltk/nltk/collocations.pys Bsi(Rtrangetlen(RR((RRs'/p/zhu/06/nlp/nltk/nltk/collocations.pyt_ngram_freqdist@scCstS((tFalse(tngramtfreq((s'/p/zhu/06/nlp/nltk/nltk/collocations.pytDscCs\xU|iiƒD]D\}}|||ƒo(y|i|=WqTtj oqTXqqWdS(s‡Generic filter removes ngrams from the frequency distribution if the function returns True when passed an ngram tuple. N(R titemstKeyError(R tfnRR((s'/p/zhu/06/nlp/nltk/nltk/collocations.pyt _apply_filterDs cs|i‡fd†ƒdS(sARemoves candidate ngrams which have frequency less than min_freq.cs |ˆjS(((tngR(tmin_freq(s'/p/zhu/06/nlp/nltk/nltk/collocations.pyRQsN(R!(R R#((R#s'/p/zhu/06/nlp/nltk/nltk/collocations.pytapply_freq_filterOscs|i‡fd†ƒdS(s`Removes candidate ngrams (w1, w2, ...) where fn(w1, w2, ...) evaluates to True. cs ˆ|ŒS(((R"tf(R (s'/p/zhu/06/nlp/nltk/nltk/collocations.pyRWsN(R!(R R ((R s'/p/zhu/06/nlp/nltk/nltk/collocations.pytapply_ngram_filterSscs|i‡fd†ƒdS(smRemoves candidate ngrams (w1, w2, ...) where any of (fn(w1), fn(w2), ...) evaluates to True. cst‡fd†|DƒƒS(c3sx|]}ˆ|ƒVqWdS(N((Rtw(R (s'/p/zhu/06/nlp/nltk/nltk/collocations.pys ]s(tany(R"R%(R (s'/p/zhu/06/nlp/nltk/nltk/collocations.pyR]sN(R!(R R ((R s'/p/zhu/06/nlp/nltk/nltk/collocations.pytapply_word_filterYsccsFx?|iD]4}|i||Œ}|dj o||fVq q WdS(sbGenerates of (ngram, score) pairs as determined by the scoring function provided. N(R t score_ngramtNone(R tscore_fnttuptscore((s'/p/zhu/06/nlp/nltk/nltk/collocations.pyt _score_ngrams_s   cCs%t|i|ƒdtdƒdtƒS(s‘Returns a sequence of (ngram, score) pairs ordered from highest to lowest score, as determined by the scoring function provided. tkeyitreverse(tsortedR/t _itemgettertTrue(R R,((s'/p/zhu/06/nlp/nltk/nltk/collocations.pyt score_ngramshscCs2g}|i|ƒ| D]\}}||q~S(s;Returns the top n ngrams when scored by the given function.(R5(R R,Rt_[1]tpts((s'/p/zhu/06/nlp/nltk/nltk/collocations.pytnbestosccs;x4|i|ƒD]#\}}||jo |VqPqWdS(s}Returns a sequence of ngrams, ordered by decreasing score, whose scores each exceed the given minimum score. N(R5(R R,t min_scoreRR.((s'/p/zhu/06/nlp/nltk/nltk/collocations.pyt above_scoress    (t__name__t __module__t__doc__R t classmethodRt staticmethodRR!R$R&R)R/R5R9R;(((s'/p/zhu/06/nlp/nltk/nltk/collocations.pyR*s      tBigramCollocationFindercBs&eZdZed„ƒZd„ZRS(s»A tool for the finding and ranking of bigram collocations or other association measures. It is often useful to use from_words() rather than constructing an instance directly. cCsvtƒ}tƒ}xTt|ddtƒD]=\}}|i|ƒ|tj o|i||fƒq(q(W|||ƒS(s[Construct a BigramCollocationFinder for all bigrams in the given sequence. it pad_right(RRR4tincR+(RRtwfdtbfdtw1tw2((s'/p/zhu/06/nlp/nltk/nltk/collocations.pyR „s     cCsa|iiƒ}|i||f}|pdSn|i|}|i|}||||f|ƒS(sWReturns the score for a given bigram using the given scoring function. N(RtNR (R R,RFRGtn_alltn_iitn_ixtn_xi((s'/p/zhu/06/nlp/nltk/nltk/collocations.pyR*’s  (R<R=R>R?R R*(((s'/p/zhu/06/nlp/nltk/nltk/collocations.pyRA~stTrigramCollocationFindercBs8eZdZd„Zed„ƒZd„Zd„ZRS(s»A tool for the finding and ranking of bigram collocations or other association measures. It is often useful to use from_words() rather than constructing an instance directly. cCs)ti|||ƒ||_||_dS(s¥Construct a TrigramCollocationFinder, given FreqDists for appearances of words, bigrams, two words with any word between them, and trigrams. N(RR t wildcard_fdt bigram_fd(R RRORNt trigram_fd((s'/p/zhu/06/nlp/nltk/nltk/collocations.pyR ¥s c CsÑtƒ}tƒ}tƒ}tƒ}x—t|ddtƒD]€\}}}|i|ƒ|tjoq:n|i||fƒ|tjoq:n|i||fƒ|i|||fƒq:W|||||ƒS(s]Construct a TrigramCollocationFinder for all trigrams in the given sequence. iRB(RRR4RCR+( RRRDtwildfdREttfdRFRGtw3((s'/p/zhu/06/nlp/nltk/nltk/collocations.pyR ®s       cCst|i|iƒS(s¸Constructs a bigram collocation finder with the bigram and unigram data from this finder. Note that this does not include any filtering applied to this finder. (RARRO(R ((s'/p/zhu/06/nlp/nltk/nltk/collocations.pyt bigram_finderÃsc Cs¹|iiƒ}|i|||f}|pdSn|i||f}|i||f}|i||f} |i|} |i|} |i|} ||||| f| | | f|ƒS(sXReturns the score for a given trigram using the given scoring function. N(RRHR RORN( R R,RFRGRSRItn_iiitn_iixtn_ixitn_xiitn_ixxtn_xixtn_xxi((s'/p/zhu/06/nlp/nltk/nltk/collocations.pyR*Ês     (R<R=R>R R?R RTR*(((s'/p/zhu/06/nlp/nltk/nltk/collocations.pyRMŸs   csrddkl}l}l}|d jo |i}n|d jo |i}nddkl}|i i dƒ‰‡fd†}xê|i i ƒD]Ù}g}|i i |ƒD]} || i ƒq®~} ti| ƒ} | idƒ| i|ƒ|GHdGg} | i|dƒD]} | d i| ƒq~ GHd |i||| i|ƒƒ|| i|ƒƒƒfGHq‘Wd S( s>Finds trigram collocations in the files of the WebText corpus.iÿÿÿÿ(Rtspearman_correlationtranks_from_scores(tcorpustenglishcs#t|ƒdjp|iƒˆjS(i(Rtlower(R'(t ignored_words(s'/p/zhu/06/nlp/nltk/nltk/collocations.pyRêsis it s Correlation to %s: %0.4fN(t nltk.metricsRR\R]R+tlikelihood_ratiotraw_freqtnltkR^t stopwordsRtwebtexttfilesR`RAR R$R)R9tjoinR<R5(tscorertcompare_scorerRR\R]R^t word_filtertfileR6twordRtcft_[2]R-((Ras'/p/zhu/06/nlp/nltk/nltk/collocations.pytdemoÞs*    ,  9 t__main__(RsBigramAssocMeasures.iitbigram_measuresttrigram_measures(R>t itertoolsR toperatorRR3tnltk.probabilityRt nltk.utilRRcRRRtnltk.metrics.spearmantobjectRRARMR+RrRtRuR<tsystevaltargvRkt IndexErrorRlt__all__(((s'/p/zhu/06/nlp/nltk/nltk/collocations.pyss4  T!?