在 R 库（tm）中，我如何获得带下划线的 NGRAMS 输出

Question

Below is my code where I am creating bigrams from text data. The output I am getting is fine except that I need the field names to have an underscore so that I can use these as variables for a model.

text<- c("Since I love to travel, this is what I rely on every time.", 
        "I got the rewards card for the no international transaction fee", 
        "I got the rewards card mainly for the flight perks",
        "Very good card, easy application process, and no international 
transaction fee",
        "The customer service is outstanding!",
        "My wife got the rewards card for the gift cards and international 
transaction fee.She loves it") 
df<- data.frame(text) 


library(tm)
corpus<- Corpus(DataframeSource(df))
corpus<- tm_map(corpus, content_transformer(tolower))
corpus<- tm_map(corpus, removePunctuation)
corpus<- tm_map(corpus, removeWords, stopwords("english"))
corpus<- tm_map(corpus, stripWhitespace)


BigramTokenizer<-
  function(x)
    unlist(lapply(ngrams(words(x),2),paste,collapse=" "),use.names=FALSE)

dtm<- DocumentTermMatrix(corpus, control= list(tokenize= BigramTokenizer))

sparse<- removeSparseTerms(dtm,.80)
dtm2<- as.matrix(sparse)
dtm2

Here is what the output looks like:

    Terms
Docs got rewards international transaction rewards card transaction fee
   1           0                         0            0               0
   2           1                         1            1               1
   3           1                         0            1               0
   4           0                         1            0               1
   5           0                         0            0               0
   6           1                         1            1               0

How do I make the field names like got_rewards instead of got rewards

Answer 1

This is not a really tm specific question I guess. Anyway, you can set collapse="_" in your code or modify the column names after the fact like so:

colnames(dtm2) <- gsub(" ", "_", colnames(dtm2), fixed = TRUE)
dtm2
    Terms
Docs got_rewards international_transaction rewards_card transaction_fee
   1           0                         0            0               0
   2           1                         1            1               1
   3           1                         0            1               0
   4           0                         1            0               1
   5           0                         0            0               0
   6           1                         1            1               0