title: How to convert a dict to an array with the key value to be a new column
body: <p>I have a dict like this:</p>
  
  <pre><code>{'ABC': array([
           [ 0.,1.,2.],
           [ 3.,4.,5.],
           [ 6.,7.,8.]]),
          array([
           [ 0.,1.,2.],
           [ 3.,4.,5.],
           [ 6.,7.,8.]])
   'DEF': array([
           [ 0.,1.,2.],
           [ 3.,4.,5.],
           [ 6.,7.,8.]]),
          array([
           [ 0.,1.,2.],
           [ 3.,4.,5.],
           [ 6.,7.,8.]])}
  </code></pre>
  
  <p>and I want to have a new like this:</p>
  
  <pre><code>['ABC','ABC','DEF','DEF']
  </code></pre>
  
  <p>with each key corresponding to each element in the value and get duplicated.</p>
  
  <p>I tried:</p>
  
  <pre><code>[(key,val) for (key,val) in d1.items()]
  </code></pre>
  
  <p>but the key didn't get duplicated </p>