title: julia create an empty dataframe and append rows to it
body: <p>I am trying out the Julia DataFrames module. I am interested in it so I can use it to plot simple simulations in Gadfly. I want to be able to iteratively add rows to the dataframe and I want to initialize it as empty. </p>
  
  <p>The tutorials/documentation on how to do this is sparse (most documentation describes how to analyse imported data). </p>
  
  <p>To append to a nonempty dataframe is straightforward: </p>
  
  <pre><code>df = DataFrame(A = [1, 2], B = [4, 5])
  push!(df, [3 6])
  </code></pre>
  
  <p>This returns. </p>
  
  <pre><code>3x2 DataFrame
  | Row | A | B |
  |-----|---|---|
  | 1   | 1 | 4 |
  | 2   | 2 | 5 |
  | 3   | 3 | 6 |
  </code></pre>
  
  <p>But for an empty init I get errors. </p>
  
  <pre><code>df = DataFrame(A = [], B = [])
  push!(df, [3, 6])
  </code></pre>
  
  <p>Error message: </p>
  
  <pre><code>ArgumentError("Error adding 3 to column :A. Possible type mis-match.")
  while loading In[220], in expression starting on line 2
  </code></pre>
  
  <p>What is the best way to initialize an empty Julia DataFrame such that you can iteratively add items to it later in a for loop?</p>