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I am new to python and practising with examples from book.
Can anyone explain why when I am trying to stem some example with this code nothing is changed?
>>> from nltk.stem import PorterStemmer
>>> stemmer=PorterStemmer()
>>> stemmer.stem('numpang wifi stop gadget shopping')
'numpang wifi stop gadget shopping'
But when I do this it works
>>> stemmer.stem('shopping')
'shop'
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Snowball stemmer: This algorithm is also known as the Porter2 stemming algorithm. It is almost universally accepted as better than the Porter stemmer, even being acknowledged as such by the individual who created the Porter stemmer.
The Porter stemming algorithm (or 'Porter stemmer') is a process for removing the commoner morphological and inflexional endings from words in English. Its main use is as part of a term normalisation process that is usually done when setting up Information Retrieval systems.
Lancaster Stemming Algorithm Like the Porter stemmer, the Lancaster stemmer consists of a set of rules where each rule specifies either deletion or replacement of an ending. Also, some rules are restricted to intact words, and some rules are applied iteratively as the word goes through them.
try this:
res = ",".join([ stemmer.stem(kw) for kw in 'numpang wifi stop gadget shopping'.split(" ")])
the problem is that, probably, that stemmer works on single words. your string has no "root" word, while the single word "shopping" has the root "shop". so you'll have to compute the stemming separately
edit:
from their source code ->
Stemming algorithms attempt to automatically remove suffixes (and in some
cases prefixes) in order to find the "root word" or stem of a given word. This
is useful in various natural language processing scenarios, such as search.
so i guess you are indeed forced to split your string by yourself
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