title: How clean data in two columns of a csv file, with many rows as documents
body: <p>I need to clean textual data from two columns (say c(8,9)) of a cvs file with around 800 rows, where each row represent a different document, containing comments from interviewees on a company. I need to apply the stopwords, but I don't know how to use tm functions on those rows of these two columns.</p>
  
  <pre><code>library(tm)
  setwd("C:\\temp")
  netf &lt;- read.csv2("netflix.csv")
  corp &lt;-tm_map(netf, c(8,9), removeWords, stopwords("english"))
  </code></pre>
  
  <blockquote>
    <p>Error in UseMethod("tm_map",x):
    no applicable method for "tm_map" applied to an object of class "data.frame"</p>
  </blockquote>
  
  <p>I would like to get the two columns with their 800 rows cleaned by stopwords</p>