title: Numpy import from CSV and convert columns to float
body: <p>ok, so i have a numpy array loaded from a CSV file,
  the array looks like : </p>
  
  <pre><code>array([['0', '3', '22', ..., '7.25', '1', '0'],
         ['1', '1', '38', ..., '71.2833', '0', '0'],
         ['1', '3', '26', ..., '7.925', '1', '0'],
         ..., 
         ['0', '3', '', ..., '23.45', '1', '0'],
         ['1', '1', '26', ..., '30', '0', '0'],
         ['0', '3', '32', ..., '7.75', '0', '0']], 
        dtype='|S8')
  </code></pre>
  
  <p>I want to convert the array elements to float but i'm having this error</p>
  
  <pre><code>data2 = np.array(data).astype(np.float)
  
  Traceback (most recent call last):
    File "&lt;input&gt;", line 1, in &lt;module&gt;
  ValueError: could not convert string to float: 
  </code></pre>
  
  <p>is there a way to solve this problem with numpy or pandas ?</p>