title: Memory error while converting list to numpy array
body: <p>I've got a total of around 7000 images from which I'm extracted HoG features. I then want to convert the list into an np array for further processing. But I get a memory error during the convertion.</p>
  
  <p>Here's the relevant part of my code:</p>
  
  <pre><code>from skimage import data, io, filter, color, exposure
  from skimage.feature import hog
  from skimage.transform import resize
  import matplotlib.pyplot as plt
  import numpy as np
  
  tmp_hogs = [] # this is the list I need to convert into a numpy array
  for group in samplegroups:
      for myimg in group:
          curr_img = np.array(myimg, dtype=float)
          imgs.append(curr_img)
          fd, hog_image = hog(curr_img, orientations=8, pixels_per_cell=(4, 4),
                   cells_per_block=(1, 1), visualise=True, normalise=True)
          tmp_hogs.append(fd)
  
  img_hogs = np.array(tmp_hogs, dtype =float) 
  </code></pre>
  
  <p>The error I get is:</p>
  
  <pre><code>Exception in thread Thread-1:
  Traceback (most recent call last):
    File "C:\Users\app\anacondasoftware\lib\threading.py", line 810, in __bootstrap_inner
      self.run()
    File "C:\Users\app\anacondasoftware\lib\site-packages\spyderlib\widgets\externalshell\monitor.py", line 582, in run
      already_pickled=True)
    File "C:\Users\app\anacondasoftware\lib\site-packages\spyderlib\utils\bsdsocket.py", line 45, in write_packet
      nsend -= temp_fail_retry(socket.error, sock.send, sent_data)
    File "C:\Users\app\anacondasoftware\lib\site-packages\spyderlib\utils\bsdsocket.py", line 25, in temp_fail_retry
      return fun(*args)
  error: [Errno 10054] An existing connection was forcibly closed by the remote host
  
  Traceback (most recent call last):
    File "C:\Users\app\Documents\Python Scripts\gbc_carclassify.py", line 63, in &lt;module&gt;
      img_hogs = np.array(tmp_hogs, dtype =float) 
  MemoryError
  </code></pre>
  
  <p>How can I fix it?</p>