NLTK树数据结构,查找节点,它的父节点或子节点

Question

我使用nltk的Tree数据结构来处理parsetree字符串.

from nltk.tree import Tree
parsed = Tree('(ROOT (S (NP (PRP It)) (VP (VBZ is) (ADJP (RB so) (JJ nice))) (. .)))')

但是,数据结构似乎有限.是否可以通过它的字符串值获取节点然后导航到顶部或底部？

例如,假设您想要获取字符串值为"nice"的节点,然后查看其父节点,子节点等是什么.是否可以通过nltk的树实现？

Answer 1

对于NLTK 3.0,您希望使用ParentedTree子类.

http://www.nltk.org/api/nltk.html#nltk.tree.ParentedTree

使用您给出的示例树,创建ParentedTree并搜索所需的节点:

from nltk.tree import ParentedTree
ptree = ParentedTree.fromstring('(ROOT (S (NP (PRP It)) \
        (VP (VBZ is) (ADJP (RB so) (JJ nice))) (. .)))')

leaf_values = ptree.leaves()

if 'nice' in leaf_values:
    leaf_index = leaf_values.index('nice')
    tree_location = ptree.leaf_treeposition(leaf_index)
    print tree_location
    print ptree[tree_location]

您可以直接遍历树以获取子树.parent()方法用于查找给定子树的父树.

这是一个为子和父使用更深层树的示例:

from nltk.tree import ParentedTree
ptree = ParentedTree.fromstring('(ROOT (S (NP (JJ Congressional) \
    (NNS representatives)) (VP (VBP are) (VP (VBN motivated) \
    (PP (IN by) (NP (NP (ADJ shiny) (NNS money))))))) (. .))')

def traverse(t):
    try:
        t.label()
    except AttributeError:
        return
    else:

        if t.height() == 2:   #child nodes
            print t.parent()
            return

        for child in t:
            traverse(child)

traverse(ptree)