dtm_chisq {udpipe}

Compare term usage across 2 document groups using the Chi-square Test for Count Data

Description

Perform a chisq.test to compare if groups of documents have more prevalence of specific terms.
The function looks to each term in the document term matrix and applies a chisq.test comparing the frequency of occurrence of each term compared to the other terms in the document group.

Usage

dtm_chisq(dtm, groups, correct = TRUE, ...)

Arguments

dtm

a document term matrix: an object returned by document_term_matrix

groups

a logical vector with 2 groups (TRUE / FALSE) where the size of the groups vector is the same as the number of rows of dtm and where element i corresponds row i of dtm

correct

passed on to chisq.test

...

further arguments passed on to chisq.test

Value

a data.frame with columns term, chisq, p.value, freq, freq_true, freq_false indicating for each term in the dtm, how frequently it occurs in each group, the Chi-Square value and it's corresponding p-value.

Examples

data(brussels_reviews_anno)
##
## Which nouns occur in text containing the term 'centre'
##
x <- subset(brussels_reviews_anno, xpos == "NN" & language == "fr")
x <- x[, c("doc_id", "lemma")]
x <- document_term_frequencies(x)
dtm <- document_term_matrix(x)
relevant <- dtm_chisq(dtm, groups = dtm[, "centre"] > 0)
head(relevant, 10)

##
## Which adjectives occur in text containing the term 'hote'
##
x <- subset(brussels_reviews_anno, xpos == "JJ" & language == "fr")
x <- x[, c("doc_id", "lemma")]
x <- document_term_frequencies(x)
dtm <- document_term_matrix(x)

group <- subset(brussels_reviews_anno, lemma %in% "hote")
group <- rownames(dtm) %in% group$doc_id
relevant <- dtm_chisq(dtm, groups = group)
head(relevant, 10)


## Not run: 
# do not show scientific notation of the p-values
options(scipen = 100)
head(relevant, 10)

## End(Not run)