title: How to combine two vectors into a data frame
body: <p>I have two vectors like this</p>
  
  <pre><code> x &lt;-c(1,2,3)
   y &lt;-c(100,200,300)
   x_name &lt;- "cond"
   y_name &lt;- "rating"
  </code></pre>
  
  <p>I'd like to output the dataframe like this:</p>
  
  <pre><code>&gt; print(df)
        cond rating
        1  x 1 
        2  x 2
        3  x 3
        4  y 100
        5  y 200
        6  y 300
  </code></pre>
  
  <p>What's the way to do it?</p>