title: How can I replace characters in a dataframe using dplyr?
body: <p>I have a dataframe where one of the columns have "MISSING" values along with numeric values, which I want to replace with NA. I know I could do it outside dplyr, but I want to keep it in <code>dplyr</code> toolchain.</p>
  
  <pre><code>read.csv('data.csv', header=F) %&gt;% 
    select(V1,V4) %&gt;% 
    mutate(V4=replace(V4, "MISSING", "NA")) 
  </code></pre>
  
  <p>but this is throwing an error:</p>
  
  <pre><code>Error in mutate_impl(.data, dots) : 
    Column `V4` must be length 30681 (the number of rows) or one, not 30682
  </code></pre>
  
  <p>Data</p>
  
  <pre><code>structure(list(V1 = c("01/01/1933", "01/02/1933", "01/03/1933", 
  "01/04/1933", "01/05/1933"), V4 = c("MISSING", "MISSING", "MISSING", 
  "MISSING", "MISSING")), .Names = c("V1", "V4"), class = c("data.table", 
  "data.frame"), row.names = c(NA, -5L), .internal.selfref = &lt;pointer: 0x10280cf78&gt;)
  </code></pre>