How to convert a text to lower case using tm package? I am using the below R code to convert text to lower case:

movie_Clean &lt;- tm_map(movie_Clean, content_transformer(tolower))


However I end up getting the below error:


  Error in FUN(content(x), ...) :    invalid input 'I just wanna watch
  Jurassic World í ½í¸«' in 'utf8towcs'.


Please help how to overcome this error.
This seems like an encoding error. Try adding the line 

Encoding(movie_Clean)  &lt;- "UTF-8"


before you lowercase the data. Check out this answer for a little context: https://stackoverflow.com/a/28340080/4539807