title: Vector from tibble has length 0
body: <p>I have a tibble ('df') with</p>
  
  <pre><code>&gt; dim(df)
  [1]  55 144
  </code></pre>
  
  <p>of which I extract a vector <code>test &lt;- c(df[,39])</code>. I would expect the following result:</p>
  
  <pre><code>&gt; length(test)
  [1] 55
  </code></pre>
  
  <p>as I basically took column 39 from my tibble. Instead, I get</p>
  
  <pre><code>&gt; length(test)
  [1] 1
  </code></pre>
  
  <p>Now, <code>class(test)</code> yielded <code>list</code>, so I thought the class might be the reason; however, with class set to <code>char</code>, I get the same result.</p>
  
  <p>I'm especially confused since <code>length(df[39,])</code> yields <code>[1] 155</code>.</p>
  
  <p>Background is I am searching in the vector using <code>grep</code>, which doesn't work with a vector taken from a column. Of course, as I am trying to recode all lines in my tibble, I can recode them by row instead of by column, so I think there is a workaround. However, <strong>what causes R to assume that <code>test</code> has length 1? What is the difference in the treatment of rows and columns?</strong></p>