CODEWITHSUNDEEP
treenltk
Roy Smith
Roy Smith

Reputation: 2163

How to navigate a nltk.tree.Tree?

I've chunked a sentence using:

grammar = '''                                                                                                              
    NP:                                                                                                                    
       {<DT>*(<NN.*>|<JJ.*>)*<NN.*>}                                                                                       
     NVN:                                                                                                                  
       {<NP><VB.*><NP>}                                                                                                    
    '''
chunker = nltk.chunk.RegexpParser(grammar)
tree = chunker.parse(tagged)
print tree

The result looks like:

(S
  (NVN
    (NP The_Pigs/NNS)
    are/VBP
    (NP a/DT Bristol-based/JJ punk/NN rock/NN band/NN))
  that/WDT
  formed/VBN
  in/IN
  1977/CD
  ./.)

But now I'm stuck trying to figure out how to navigate that. I want to be able to find the NVN subtree, and access the left-side noun phrase ("The_Pigs"), the verb ("are") and the right-side noun phrase ("a Bristol-based punk rock band"). How do I do that?

Upvotes: 25

Views: 27972

Answers (4)

matt
matt

Reputation: 823

Try this:

for a in tree:
        if type(a) is nltk.Tree:
            if a.node == 'NVN': # This climbs into your NVN tree
                for b in a:
                    if type(b) is nltk.Tree and b.node == 'NP':
                        print b.leaves() # This outputs your "NP"
                    else:
                        print b # This outputs your "VB.*"

It outputs this:

[('The_Pigs', 'NNS')]

('are', 'VBP')

[('a', 'DT'), ('Bristol-based', 'JJ'), ('punk', 'NN'), ('rock', 'NN'), ('band', 'NN')]

Upvotes: 5

redreamality
redreamality

Reputation: 1164

here's a code sample for generating all the subtrees with a label 'NP'

def filt(x):
    return x.label()=='NP'

for subtree in t.subtrees(filter =  filt): # Generate all subtrees
    print subtree

for siblings, you might wanna take a look at the method ParentedTree.left_siblings()

for more details, here are some useful links.

http://www.nltk.org/howto/tree.html #some basic usage and example http://nbviewer.ipython.org/github/gmonce/nltk_parsing/blob/master/1.%20NLTK%20Syntax%20Trees.ipynb #a notebook playwith these methods

http://www.nltk.org/_modules/nltk/tree.html #all api with source

Upvotes: 7

Melroy van den Berg
Melroy van den Berg

Reputation: 3156

Try:

ROOT = 'ROOT'
tree = ...
def getNodes(parent):
    for node in parent:
        if type(node) is nltk.Tree:
            if node.label() == ROOT:
                print "======== Sentence ========="
                print "Sentence:", " ".join(node.leaves())
            else:
                print "Label:", node.label()
                print "Leaves:", node.leaves()

            getNodes(node)
        else:
            print "Word:", node

getNodes(tree)

Upvotes: 19

Peter Enns
Peter Enns

Reputation: 610

You could, of course, write your own depth first search... but there is an easier (better) way. If you want every subtree rooted at NVM, use Tree's subtree method with the filter parameter defined.

>>> print t
(S
    (NVN
        (NP The_Pigs/NNS)
        are/VBP
        (NP a/DT Bristol-based/JJ punk/NN rock/NN band/NN))
    that/WDT
    formed/VBN
    in/IN
    1977/CD
    ./.)
>>> for i in t.subtrees(filter=lambda x: x.node == 'NVN'):
...     print i
... 
(NVN
    (NP The_Pigs/NNS)
    are/VBP
    (NP a/DT Bristol-based/JJ punk/NN rock/NN band/NN))

Upvotes: 9

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