Collocations {text2vec}

Collocations model.

Description

Creates Collocations model which can be used for phrase extraction.

Usage

Collocations

Format

R6Class object.

Fields

collocation_stat

data.table with collocations(phrases) statistics. Useful for filtering non-relevant phrases

Usage

For usage details see Methods, Arguments and Examples sections.

model = Collocations$new(vocabulary = NULL, collocation_count_min = 50, pmi_min = 5, gensim_min = 0,
                         lfmd_min = -Inf, llr_min = 0, sep = "_")
model$partial_fit(it, ...)
model$fit(it, n_iter = 1, ...)
model$transform(it)
model$prune(pmi_min = 5, gensim_min = 0, lfmd_min = -Inf, llr_min = 0)
model$collocation_stat

Methods

$new(vocabulary = NULL, collocation_count_min = 50, sep = "_")

Constructor for Collocations model. For description of arguments see Arguments section.

$fit(it, n_iter = 1, ...)

fit Collocations model to input iterator it. Iterating over input iterator it n_iter times, so hierarchically can learn multi-word phrases. Invisibly returns collocation_stat.

$partial_fit(it, ...)

iterates once over data and learns collocations. Invisibly returns collocation_stat. Workhorse for $fit()

$transform(it)

transforms input iterator using learned collocations model. Result of the transformation is new itoken or itoken_parallel iterator which will produce tokens with phrases collapsed into single token.

$prune(pmi_min = 5, gensim_min = 0, lfmd_min = -Inf, llr_min = 0)

filter out non-relevant phrases with low score. User can do it directly by modifying collocation_stat object.

Arguments

model

A Collocation model object

n_iter

number of iteration over data

pmi_min, gensim_min, lfmd_min, llr_min

minimal scores of the corresponding statistics in order to collapse tokens into collocation:

• pointwise mutual information

• "gensim" scores - https://radimrehurek.com/gensim/models/phrases.html adapted from word2vec paper

• log-frequency biased mutual dependency

• Dunning's logarithm of the ratio between the likelihoods of the hypotheses of dependence and independence

See https://aclanthology.org/I05-1050/ for details. Also see data in model$collocation_stat for better intuition

it

An input itoken or itoken_parallel iterator

vocabulary

text2vec_vocabulary - if provided will look for collocations consisted of only from vocabulary

Examples

library(text2vec)
data("movie_review")

preprocessor = function(x) {
  gsub("[^[:alnum:]\\s]", replacement = " ", tolower(x))
}
sample_ind = 1:100
tokens = word_tokenizer(preprocessor(movie_review$review[sample_ind]))
it = itoken(tokens, ids = movie_review$id[sample_ind])
system.time(v <- create_vocabulary(it))
v = prune_vocabulary(v, term_count_min = 5)

model = Collocations$new(collocation_count_min = 5, pmi_min = 5)
model$fit(it, n_iter = 2)
model$collocation_stat

it2 = model$transform(it)
v2 = create_vocabulary(it2)
v2 = prune_vocabulary(v2, term_count_min = 5)
# check what phrases model has learned
setdiff(v2$term, v$term)
# [1] "main_character"  "jeroen_krabb"    "boogey_man"      "in_order"
# [5] "couldn_t"        "much_more"       "my_favorite"     "worst_film"
# [9] "have_seen"       "characters_are"  "i_mean"          "better_than"
# [13] "don_t_care"      "more_than"       "look_at"         "they_re"
# [17] "each_other"      "must_be"         "sexual_scenes"   "have_been"
# [21] "there_are_some"  "you_re"          "would_have"      "i_loved"
# [25] "special_effects" "hit_man"         "those_who"       "people_who"
# [29] "i_am"            "there_are"       "could_have_been" "we_re"
# [33] "so_bad"          "should_be"       "at_least"        "can_t"
# [37] "i_thought"       "isn_t"           "i_ve"            "if_you"
# [41] "didn_t"          "doesn_t"         "i_m"             "don_t"

# and same way we can create document-term matrix which contains
# words and phrases!
dtm = create_dtm(it2, vocab_vectorizer(v2))
# check that dtm contains phrases
which(colnames(dtm) == "jeroen_krabb")