spaCy/spacy/pipeline/_parser_internals/nonproj.pyx

# cython: infer_types=True
"""Implements the projectivize/deprojectivize mechanism in Nivre & Nilsson 2005
for doing pseudo-projective parsing implementation uses the HEAD decoration
scheme.
"""
from copy import copy

from cython.operator cimport dereference as deref
from cython.operator cimport preincrement as incr
from libc.limits cimport INT_MAX
from libc.stdlib cimport abs
from libcpp cimport bool
from libcpp.string cimport string, to_string
from libcpp.unordered_set cimport unordered_set
from libcpp.vector cimport vector

from ...tokens.doc cimport Doc, set_children_from_heads

from ...errors import Errors

DELIMITER = '||'


def ancestors(tokenid, heads):
    # Returns all words going from the word up the path to the root. The path
    # to root cannot be longer than the number of words in the  sentence. This
    # function ends after at most len(heads) steps, because it would otherwise
    # loop indefinitely on cycles.
    head = tokenid
    cnt = 0
    while heads[head] != head and cnt < len(heads):
        head = heads[head]
        cnt += 1
        yield head
        if head is None:
            break


def contains_cycle(heads):
    # in an acyclic tree, the path from each word following the head relation
    # upwards always ends at the root node
    for tokenid in range(len(heads)):
        seen = set([tokenid])
        for ancestor in ancestors(tokenid, heads):
            if ancestor in seen:
                return seen
            seen.add(ancestor)
    return None


def is_nonproj_arc(tokenid, heads):
    cdef vector[int] c_heads = _heads_to_c(heads)
    return _is_nonproj_arc(tokenid, c_heads)


cdef bool _is_nonproj_arc(int tokenid, const vector[int]& heads) nogil except *:
    # definition (e.g. Havelka 2007): an arc h -> d, h < d is non-projective
    # if there is a token k, h < k < d such that h is not
    # an ancestor of k. Same for h -> d, h > d
    head = heads[tokenid]
    if head == tokenid:  # root arcs cannot be non-projective
        return False
    elif head < 0:  # unattached tokens cannot be non-projective
        return False

    cdef int start, end
    if head < tokenid:
        start, end = (head+1, tokenid)
    else:
        start, end = (tokenid+1, head)
    for k in range(start, end):
        if not _has_head_as_ancestor(k, head, heads):
            return True
    return False


cdef bool _has_head_as_ancestor(int tokenid, int head, const vector[int]& heads) nogil except *:
    ancestor = tokenid
    cdef unordered_set[int] seen_tokens
    seen_tokens.insert(ancestor)
    while True:
        # Reached the head or a disconnected node
        if heads[ancestor] == head or heads[ancestor] < 0:
            return True
        # Reached the root
        if heads[ancestor] == ancestor:
            return False
        ancestor = heads[ancestor]
        result = seen_tokens.insert(ancestor)
        # Found cycle
        if not result.second:
            raise_domain_error(heads_to_string(heads))

    return False


cdef string heads_to_string(const vector[int]& heads) nogil:
    cdef vector[int].const_iterator citer
    cdef string cycle_str

    cycle_str.append("Found cycle in dependency graph: [")

    # FIXME: Rewrite using ostringstream when available in Cython.
    citer = heads.const_begin()
    while citer != heads.const_end():
        if citer != heads.const_begin():
            cycle_str.append(", ")
        cycle_str.append(to_string(deref(citer)))
        incr(citer)
    cycle_str.append("]")

    return cycle_str


def is_nonproj_tree(heads):
    cdef vector[int] c_heads = _heads_to_c(heads)
    # a tree is non-projective if at least one arc is non-projective
    return any(_is_nonproj_arc(word, c_heads) for word in range(len(heads)))


def decompose(label):
    return label.partition(DELIMITER)[::2]


def is_decorated(label):
    return DELIMITER in label


def count_decorated_labels(gold_data):
    freqs = {}
    for example in gold_data:
        proj_heads, deco_deps = projectivize(example.get_aligned("HEAD"),
                                             example.get_aligned("DEP"))
        # set the label to ROOT for each root dependent
        deco_deps = [
            'ROOT' if head == i else deco_deps[i]
            for i, head in enumerate(proj_heads)
        ]
        # count label frequencies
        for label in deco_deps:
            if is_decorated(label):
                freqs[label] = freqs.get(label, 0) + 1
    return freqs


def projectivize(heads, labels):
    # Use the algorithm by Nivre & Nilsson 2005. Assumes heads to be a proper
    # tree, i.e. connected and cycle-free. Returns a new pair (heads, labels)
    # which encode a projective and decorated tree.
    proj_heads = copy(heads)

    cdef int new_head
    cdef vector[int] c_proj_heads = _heads_to_c(proj_heads)
    cdef int smallest_np_arc = _get_smallest_nonproj_arc(c_proj_heads)
    if smallest_np_arc == -1:  # this sentence is already projective
        return proj_heads, copy(labels)
    while smallest_np_arc != -1:
        new_head = _lift(smallest_np_arc, proj_heads)
        c_proj_heads[smallest_np_arc] = new_head
        smallest_np_arc = _get_smallest_nonproj_arc(c_proj_heads)
    deco_labels = _decorate(heads, proj_heads, labels)
    return proj_heads, deco_labels


cdef vector[int] _heads_to_c(heads):
    cdef vector[int] c_heads
    for head in heads:
        if head is None:
            c_heads.push_back(-1)
        else:
            assert head < len(heads)
            c_heads.push_back(head)
    return c_heads


cpdef deprojectivize(Doc doc):
    # Reattach arcs with decorated labels (following HEAD scheme). For each
    # decorated arc X||Y, search top-down, left-to-right, breadth-first until
    # hitting a Y then make this the new head.
    for i in range(doc.length):
        label = doc.vocab.strings[doc.c[i].dep]
        if DELIMITER in label:
            new_label, head_label = label.split(DELIMITER)
            new_head = _find_new_head(doc[i], head_label)
            doc.c[i].head = new_head.i - i
            doc.c[i].dep = doc.vocab.strings.add(new_label, allow_transient=False)
    set_children_from_heads(doc.c, 0, doc.length)
    return doc


def _decorate(heads, proj_heads, labels):
    # uses decoration scheme HEAD from Nivre & Nilsson 2005
    if (len(heads) != len(proj_heads)) or (len(proj_heads) != len(labels)):
        raise ValueError(Errors.E082.format(n_heads=len(heads),
                                            n_proj_heads=len(proj_heads),
                                            n_labels=len(labels)))
    deco_labels = []
    for tokenid, head in enumerate(heads):
        if head != proj_heads[tokenid]:
            deco_labels.append(f"{labels[tokenid]}{DELIMITER}{labels[head]}")
        else:
            deco_labels.append(labels[tokenid])
    return deco_labels


def get_smallest_nonproj_arc_slow(heads):
    cdef vector[int] c_heads = _heads_to_c(heads)
    return _get_smallest_nonproj_arc(c_heads)


cdef int _get_smallest_nonproj_arc(const vector[int]& heads) nogil except -2:
    # return the smallest non-proj arc or None
    # where size is defined as the distance between dep and head
    # and ties are broken left to right
    cdef int smallest_size = INT_MAX
    # -1 means its already projective.
    cdef int smallest_np_arc = -1
    cdef int size
    cdef int tokenid
    cdef int head

    for tokenid in range(heads.size()):
        head = heads[tokenid]
        size = abs(tokenid-head)
        if size < smallest_size and _is_nonproj_arc(tokenid, heads):
            smallest_size = size
            smallest_np_arc = tokenid
    return smallest_np_arc


cpdef int _lift(tokenid, heads):
    # reattaches a word to it's grandfather
    head = heads[tokenid]
    ghead = heads[head]
    cdef int new_head = ghead if head != ghead else tokenid
    # attach to ghead if head isn't attached to root else attach to root
    heads[tokenid] = new_head
    return new_head


def _find_new_head(token, headlabel):
    # search through the tree starting from the head of the given token
    # returns the id of the first descendant with the given label
    # if there is none, return the current head (no change)
    queue = [token.head]
    while queue:
        next_queue = []
        for qtoken in queue:
            for child in qtoken.children:
                if child.is_space:
                    continue
                if child == token:
                    continue
                if child.dep_ == headlabel:
                    return child
                next_queue.append(child)
        queue = next_queue
    return token.head