title: R Change NA values
body: <p>My data looks like this:
  <a href="http://imgur.com/8KgvWvP" rel="noreferrer">http://imgur.com/8KgvWvP</a></p>
  
  <p>I want to change the values <code>NA</code> to another value for each column. 
  For example in the column that contains <code>NA</code>, <code>Single</code> and <code>Dual</code>, I want to change all the <code>NA</code> to <code>'Single'</code>.</p>
  
  <p>I tried this code: </p>
  
  <pre><code>data_price$nbrSims &lt;- ifelse(is.na(data_price$nbrSims), 'Single', data_price$nbrSims)
  </code></pre>
  
  <p>But then my data looks like this, where <code>Dual</code> became <code>2</code> and <code>Single</code> <code>1</code>.
  <a href="http://imgur.com/TC1bIgw" rel="noreferrer">http://imgur.com/TC1bIgw</a></p>
  
  <p>How can I change the <code>NA</code> values, without changing the other values?
  Thanks in advance!</p>