class HashTfidfVectoriser:
def __init__(self, n_features):
self.hashing_vectoriser = HashingVectorizer(n_features=n_features,
alternate_sign=False)
self.tfidf_transformer = TfidfTransformer()
self.words_by_hashes_dict = {}
self.last_data = None
def words_by_hash(self, hash):
return self.words_by_hashes_dict[hash]
def fit_transform(self, data):
self.last_data = data[:]
for i in range(len(data)):
data[i] = re.sub("\d+", "", data[i])
self.words_by_hashes_dict = {}
words_list = self.hashing_vectoriser.build_analyzer()("\n".join(data))
unique_words = set(words_list)
hashes = self.hashing_vectoriser.transform(unique_words).indices
for w, h in zip(unique_words, hashes):
old_list = self.words_by_hashes_dict.get(h, [])
old_list.append(w)
self.words_by_hashes_dict[h] = old_list
return self.tfidf_transformer.fit_transform(
self.hashing_vectoriser.fit_transform(data))
def cleaner_str(s):
cleaner = HashingVectorizer(decode_error = 'ignore',
analyzer = 'word',
ngram_range = (1,1),
stop_words = 'english')
c = cleaner.build_analyzer()
s = (" ").join(c(s))
return s
# This mapping is completely stateless and the dimensionality of the output space is explicitly fixed in advance (here we use a modulo `2 ** 20` which means roughly 1M dimensions). The makes it possible to workaround the limitations of the vocabulary based vectorizer both for parallelizability and online / out-of-core learning.
# %% [markdown] {"deletable": true, "editable": true}
# The `HashingVectorizer` class is an alternative to the `CountVectorizer` (or `TfidfVectorizer` class with `use_idf=False`) that internally uses the murmurhash hash function:
# %% {"deletable": true, "editable": true}
from sklearn.feature_extraction.text import HashingVectorizer
h_vectorizer = HashingVectorizer(encoding='latin-1')
h_vectorizer
# %% [markdown] {"deletable": true, "editable": true}
# It shares the same "preprocessor", "tokenizer" and "analyzer" infrastructure:
# %% {"deletable": true, "editable": true}
analyzer = h_vectorizer.build_analyzer()
analyzer('This is a test sentence.')
# %% [markdown] {"deletable": true, "editable": true}
# We can vectorize our datasets into a scipy sparse matrix exactly as we would have done with the `CountVectorizer` or `TfidfVectorizer`, except that we can directly call the `transform` method: there is no need to `fit` as `HashingVectorizer` is a stateless transformer:
# %% {"deletable": true, "editable": true}
docs_train, y_train = train['data'], train['target']
docs_valid, y_valid = test['data'][:12500], test['target'][:12500]
docs_test, y_test = test['data'][12500:], test['target'][12500:]
# %% [markdown] {"deletable": true, "editable": true}
# The dimension of the output is fixed ahead of time to `n_features=2 ** 20` by default (nearly 1M features) to minimize the rate of collision on most classification problem while having reasonably sized linear models (1M weights in the `coef_` attribute):
# %% {"deletable": true, "editable": true}
h_vectorizer.transform(docs_train)
