我试图将我的语料库转换回 Dataframe ，但它只返回NA的。请帮助
代码：

library(wordcloud)
df <- data.frame(Description = c("I like this service very much"," this is worth it so much"))

corpus <- Corpus(VectorSource(df$Description))

corpus <- tm_map(corpus, tolower)

corpus <- tm_map(corpus, removePunctuation)
corpus <- tm_map(corpus, removeWords, c(stopwords('english')))
corpus <- tm_map(corpus, stripWhitespace)
corpus <- tm_map(corpus, stemDocument)

#a <- as.data.frame(corpus)

dataframe<-data.frame(text=unlist(sapply(corpus, `[`, "content")), 
                      stringsAsFactors=F)

预期输出：
Dataframe

'like servic much'
'worth much'