Error in .jcall()

Question

I am running the following code and receiving this error:

Error in .jcall("RWekaInterfaces", "[S", "tokenize", .jcast(tokenizer, : java.lang.NullPointerException

setwd("C:\\Users\\jbarr\\Desktop\\test)
library (tm); library (wordcloud);library (RWeka); library (tau);library(xlsx);

Comment <- read.csv("testfile.csv",stringsAsFactors=FALSE) 
str(Comment) 
review_source <- VectorSource(Comment) 

corpus <- Corpus(review_source)
corpus <- tm_map(corpus, removePunctuation)
corpus <- tm_map(corpus, removeNumbers)
corpus <- tm_map(corpus, stripWhitespace)
corpus <- tm_map(corpus, removeWords,stopwords(kind = "english"))
corpus <- tm_map(corpus, content_transformer(tolower))
corpus <- tm_map(corpus, removeWords, c("member", "advise", "inform", "informed", "caller", "call","provided", "advised")) 


dtm <- DocumentTermMatrix(corpus)
dtm2 <- as.matrix(dtm)
wordfreq <- colSums(dtm2)
wordfreq <- sort(wordfreq, decreasing=TRUE)
head(wordfreq, n=100)
wfreq <- head(wordfreq, 500)
set.seed(142)
words <- names(wfreq)
dark2 <- brewer.pal(6, "Dark2")
wordcloud(words[1:100], wordfreq[1:100], rot.per=0.35, scale=c(2.7, .4), colors=dark2, random.order=FALSE)
write.xlsx(wfreq, "C:\\Users\\jbarr\\Desktop\\test")

The interesting problem is, I have ran this code on multiple files, and only specific ones have the error.

Answer 1

Sanmeet is right - it's a problem with NAs in your data frame.

just prior to your line: review_source <- VectorSource(Comment)

insert the line below:

Comment[which(is.na(Comment))] <- "NULLVALUEENTERED"

This will change all of your NA values to the phrase NULLVALUEENTERED (feel free to change that). No more NAs, and the code should run fine.

Answer 2

You are getting the error in tokenizer due to NA in your string vector Comment

Comment <- read.csv("testfile.csv",stringsAsFactors=FALSE) 
str(Comment)     
length(Comment)
Comment = Comment[complete.cases(Comment)]
length(Comment)

Or you can also use is.na as below

Comment = Comment[!is.na(Comment)]

Now apply the preprocessing steps, create the corpus etc

Hope this helps.