以下代码在使用mutate_时出现错误

Question

制作DTM时出现以下错误

  

UseMethod（“ mutate_”）中的错误：没有适用于'mutate_'的方法   应用于“字符”类的对象

text  = charges.df$charge.desc %>% clean_text(alphanum=TRUE) 
 textdf = data.frame(docID=seq(1:length(text)), text = text, stringsAsFactors=FALSE) 
  textdf = tibble(docID=seq(1:length(text)), text = text, stringsAsFactors=FALSE)
 corpus_df = textdf %>% dplyr::sample_n(1000)   
# using just a 1000 doc sample for demo purposes

 system.time({  
   charge.dtm = corpus_df$text %>% 

        # routine to build bigram tokens with "_"
        replace_bigram(min_freq=2) 

   charge.dtm = charge.dtm$text %>% 
        casting_dtm() %>%     # dtm is cast using tidytext alone

        # processing DTMs for compactness
        preprocess_dtm(min_occur = 0.01, max_occur = 0.90) %>%     # prune dtm colms afap
        nonempty_dtm()    # routine to clean DTMs of empty rows/colms

  })    # t = 41.5 secs for 10k documents

 dim(charge.dtm)