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NLP | Part of Speech – Default Tagging

  • Last Updated : 28 Oct, 2019
Geek Week

Whats is Part-of-speech (POS) tagging ?
It is a process of converting a sentence to forms – list of words, list of tuples (where each tuple is having a form (word, tag)). The tag in case of is a part-of-speech tag, and signifies whether the word is a noun, adjective, verb, and so on.

Default tagging is a basic step for the part-of-speech tagging. It is performed using the DefaultTagger class. The DefaultTagger class takes ‘tag’ as a single argument. NN is the tag for a singular noun. DefaultTagger is most useful when it gets to work with most common part-of-speech tag. that’s why a noun tag is recommended.

Code #1 : How it works ?




# Loading Libraries
from nltk.tag import DefaultTagger
  
# Defining Tag
tagging = DefaultTagger('NN')
  
# Tagging
tagging.tag(['Hello', 'Geeks'])

Output :

[('Hello', 'NN'), ('Geeks', 'NN')]

Each tagger has a tag() method that takes a list of tokens (usually list of words produced by a word tokenizer), where each token is a single word. tag() returns a list of tagged tokens – a tuple of (word, tag).



How DefaultTagger works ?
It is a subclass of SequentialBackoffTagger and implements the choose_tag() method, having three arguments.

  • list of tokens
  • index of the current token, to choose the tag.
  • list of the previous tags

 
Code #2 : Tagging Sentences




# Loading Libraries
from nltk.tag import DefaultTagger
  
# Defining Tag
tagging = DefaultTagger('NN')
  
tagging.tag_sents([['welcome', 'to', '.'], ['Geeks', 'for', 'Geeks']])

Output :

[[('welcome', 'NN'), ('to', 'NN'), ('.', 'NN')],
 [('Geeks', 'NN'), ('for', 'NN'), ('Geeks', 'NN')]]

Note: Every tag in the list of tagged sentences (in the above code) is NN as we have used DefaultTagger class.

Code #3 : Illustrating how to untag.




from nltk.tag import untag
untag([('Geeks', 'NN'), ('for', 'NN'), ('Geeks', 'NN')])

Output :

['Geeks', 'for', 'Geeks']

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