title: Adding a returned NULL into data frame as value
body: <p>I have these vectors that I would like to make as a dataframe whilst having the 4th value also as a value instead of the 4th value being a &quot;NULL&quot; and stopping further processing</p>
  <pre><code>    a &lt;- Dataset$price1
      b &lt;- Dataset$price33
      c &lt;- Dataset$price16
      d &lt;- Dataset$price40
  
  &gt; a
  [1] 0.76
  
  &gt; b
  [1] 0.52
  
  &gt; c
  [1] 0.93
  
  &gt; d
  NULL
  
  </code></pre>
  <p>Consequently, this doesn't work</p>
  <pre><code>    test &lt;- c(a,b,c,d)
  </code></pre>
  <p><strong>Desired outcome:</strong></p>
  <pre><code>&gt; c(a,b,c,d)
  
  [1] 0.76 0.52 0.93 0
  
  </code></pre>
  <p>Thanks for any help!</p>