gensim-python矩阵市场格式中的转置参数

Question

在gensim库中，有一个MmReader类将matrix market format文件转换为python对象。有时需要transpose the matrix，因此在MmReader中引入了转置参数。在

但是，我很困惑，为什么在525-526和{}的525-526行，当transposed == False时，术语文档值和id的倒置会发生。在

熟悉信息检索中的术语文档矩阵的人能给我一些启发吗？在

class MmReader(object):
    """
    Wrap a term-document matrix on disk (in matrix-market format), and present it
    as an object which supports iteration over the rows (~documents).

    Note that the file is read into memory one document at a time, not the whole
    matrix at once (unlike scipy.io.mmread). This allows us to process corpora
    which are larger than the available RAM.
    """
    def __init__(self, input, transposed=True):
        """
        Initialize the matrix reader.

        The `input` refers to a file on local filesystem, which is expected to
        be in the sparse (coordinate) Matrix Market format. Documents are assumed
        to be rows of the matrix (and document features are columns).

        `input` is either a string (file path) or a file-like object that supports
        `seek()` (e.g. gzip.GzipFile, bz2.BZ2File).
        """
        logger.info("initializing corpus reader from %s" % input)
        self.input, self.transposed = input, transposed
        if isinstance(input, basestring):
            input = open(input)
        header = input.next().strip()
        if not header.lower().startswith('%%matrixmarket matrix coordinate real general'):
            raise ValueError("File %s not in Matrix Market format with coordinate real general; instead found: \n%s" %
                             (self.input, header))
        self.num_docs = self.num_terms = self.num_nnz = 0
        for lineno, line in enumerate(input):
            if not line.startswith('%'):
                self.num_docs, self.num_terms, self.num_nnz = map(int, line.split())
                if not self.transposed: ## line 525
                    self.num_docs, self.num_terms = self.num_terms, self.num_docs
                break
        logger.info("accepted corpus with %i documents, %i features, %i non-zero entries" %
                     (self.num_docs, self.num_terms, self.num_nnz))

    def __len__(self):
        return self.num_docs

    def __str__(self):
        return ("MmCorpus(%i documents, %i features, %i non-zero entries)" %
                (self.num_docs, self.num_terms, self.num_nnz))

    def skip_headers(self, input_file):
        """
        Skip file headers that appear before the first document.
        """
        for line in input_file:
            if line.startswith('%'):
                continue
            break

    def __iter__(self):
        """
        Iteratively yield vectors from the underlying file, in the format (row_no, vector),
        where vector is a list of (col_no, value) 2-tuples.

        Note that the total number of vectors returned is always equal to the
        number of rows specified in the header; empty documents are inserted and
        yielded where appropriate, even if they are not explicitly stored in the
        Matrix Market file.
        """
        if isinstance(self.input, basestring):
            fin = open(self.input)
        else:
            fin = self.input
            fin.seek(0)
        self.skip_headers(fin)

        previd = -1
        for line in fin:
            docid, termid, val = line.split()
            if not self.transposed:
                termid, docid = docid, termid
            docid, termid, val = int(docid) - 1, int(termid) - 1, float(val) # -1 because matrix market indexes are 1-based => convert to 0-based
            assert previd <= docid, "matrix columns must come in ascending order"
            if docid != previd:
                # change of document: return the document read so far (its id is prevId)
                if previd >= 0:
                    yield previd, document

                # return implicit (empty) documents between previous id and new id
                # too, to keep consistent document numbering and corpus length
                for previd in xrange(previd + 1, docid):
                    yield previd, []

                # from now on start adding fields to a new document, with a new id
                previd = docid
                document = []

            document.append((termid, val,)) # add another field to the current document

        # handle the last document, as a special case
        if previd >= 0:
            yield previd, document

        # return empty documents between the last explicit document and the number
        # of documents as specified in the header
        for previd in xrange(previd + 1, self.num_docs):
            yield previd, []


    def docbyoffset(self, offset):
        """Return document at file offset `offset` (in bytes)"""
        # empty documents are not stored explicitly in MM format, so the index marks
        # them with a special offset, -1.
        if offset == -1:
            return []
        if isinstance(self.input, basestring):
            fin = open(self.input)
        else:
            fin = self.input

        fin.seek(offset) # works for gzip/bz2 input, too
        previd, document = -1, []
        for line in fin:
            docid, termid, val = line.split()
            if not self.transposed: ## line 567
                termid, docid = docid, termid
            docid, termid, val = int(docid) - 1, int(termid) - 1, float(val) # -1 because matrix market indexes are 1-based => convert to 0-based
            assert previd <= docid, "matrix columns must come in ascending order"
            if docid != previd:
                if previd >= 0:
                    return document
                previd = docid

            document.append((termid, val,)) # add another field to the current document
        return document
#endclass MmReader

Answer 1

显然，transposed参数从未在最新版本的gensim中使用，其中mmreader和{}的格式相同。在

有关详细信息，开发人员在https://groups.google.com/forum/?hl=en#!topic/gensim/XC7Q_q3WcyQ中解释了