title: Turn 2D NumPy array into 1D array for plotting a histogram
body: <p>I'm trying to plot a histogram with matplotlib.
  I need to convert my one-line 2D Array </p>
  
  <pre><code>[[1,2,3,4]] # shape is (1,4)
  </code></pre>
  
  <p>into a 1D Array</p>
  
  <pre><code>[1,2,3,4] # shape is (4,)
  </code></pre>
  
  <p>How can I do this?</p>