title: How to merge multiple 2d arrays in numpy?
body: <p><strong>MWE:</strong> Suppose I have 12 2D-arrays. I want to merge them in some fixed size using loop. The following code gives the result I want to get X. Here I have concatenate 3 2D-arrays, but if I want to fixed this size according my choice using loop, how can I do this?</p>
  
  <pre><code>import numpy as np
  a1 = np.array([[0, 12, 3], [5, 8, 9]])
  a2 = np.array([[2, 13, 3], [5, 9, 9]])
  a3 = np.array([[0, 24, 4], [6, 10, 9]])
  a4 = np.array([[1, 55, 6], [4, 5, 19]])
  a5 = np.array([[1, 56, 6], [4, 01, 9]])
  a6 = np.array([[1, 57, 6], [4, 20, 9]])
  a7 = np.array([[1, 58, 6], [4, 30, 9]])
  a8 = np.array([[1, 59, 6], [4, 40, 9]])
  a9 = np.array([[1, 51, 6], [4, 60, 9]])
  a10 = np.array([[1, 34, 6], [4, 60, 9]])
  a11 = np.array([[1, 51, 62], [4, 30, 9]])
  a12 = np.array([[1, 1, 6], [4, 7, 9]]) 
  
  M=[a1,a2,a3,a4,a5,a6,a7,a8,a9,a10,a11,a12]
  d1 = np.concatenate((a1,a2,a3), 1)
  d2 = np.concatenate((a4,a5,a6), 1)
  d3 = np.concatenate((a7,a8,a9), 1)
  d4 = np.concatenate((a10,a11,a12), 1)
  X=[d1,d2,d3,d4]
  </code></pre>