title: Difference between "$i" and :$("$i") in Julia DataFrame
body: <p>When <code>i=1</code>, both <code>println(typeof(&quot;$i&quot;))</code> and <code>println(typeof(:($(&quot;$i&quot;))))</code> give <code>String</code>, and both <code>println(&quot;$i&quot;)</code> and <code>println(:($(&quot;$i&quot;)))</code> give <code>1</code>. However, the following code</p>
  <pre><code>using DataFrames
  df = DataFrame()
  i = 1
  df.:($(&quot;$i&quot;)) = [0.0]
  println(df)
  </code></pre>
  <p>works, but the following code</p>
  <pre><code>using DataFrames
  df = DataFrame()
  i = 1
  df.&quot;$i&quot; = [0.0]
  println(df)
  </code></pre>
  <p>does not work. What is wrong with the latter code?</p>