title: R data.table grepl column on another column in i
body: <p>Can I subset for when a string in column A is in column B?</p>
  
  <p>Example:</p>
  
  <pre><code>x &lt;- data.table(a=letters, y=paste0(letters,"x"))
  
  x[grepl(a, y)]
  x[like(y, a)]
  </code></pre>
  
  <p>Both return only a one row data.table of the first row and the following warning: </p>
  
  <pre><code>Warning message:
  In grepl(pattern, vector) :
    argument 'pattern' has length &gt; 1 and only the first element will be used
  </code></pre>
  
  <p>I would expect this to return all rows.</p>