title: Creating a 2d NumPy array (Python)
body: <p>NumPy newb. </p>
  
  <p>I created a simple 2d array in <strong>np_2d</strong>, below. Works great. </p>
  
  <p>Of course, I'm generally going to need to create N-d arrays by appending and/or concatenating existing arrays, so I'm trying that next. </p>
  
  <p>The np.append method (with or without the axis parameter) doesn't seem to do anything. </p>
  
  <p>My attempts to use .concantenate() and/or simply replace raw lists with np arrays also fail. </p>
  
  <p>I'm sure this is trivial to do...just not trivial for me ATM. Can someone push me in the right direction? TY.</p>
  
  <pre><code>import numpy as np
  
  # NumPy 2d array:
  np_2d = np.array([[1.73, 1.68, 1.71, 1.89, 1.79], [65.4, 59.2, 63.6, 88.4, 68.7]])
  
  print (np_2d) 
  
  # [[ 1.73  1.68  1.71  1.89  1.79]
  # [65.4  59.2  63.6  88.4  68.7 ]]
  
  print (np_2d[1]) # second list
  
  # [65.4 59.2 63.6 88.4 68.7]
  
  np_2d_again = np.array([1.1, 2.2, 3.3])
  
  np.append(np_2d_again, [4.4, 5.5, 6.6])
  print(np_2d_again)
  
  # wrong: [1.1 2.2 3.3], expect [1.1 2.2 3.3], [4.4, 5.5, 6.6]
  # or MAYBE [1.1 2.2 3.3, 4.4, 5.5, 6.6]
  
  
  np_2d_again = np.array([[1.1, 2.2, 3.3]])
  np.concatenate(np_2d_again, np.array([4.4, 5.5, 6.6]))
  
  # Nope: TypeError: only integer scalar arrays can be converted to a scalar index
  
  print(np_2d_again)
  
  np_height = np.array([1.73, 1.68, 1.71, 1.89, 1.79])
  np_weight = np.array([65.4, 59.2, 63.6, 88.4, 68.7])
  
  np2_2d_again = np.array(np_height, np_weight)
  
  # Nope: TypeError: data type not understood
  
  height = [1.73, 1.68, 1.71, 1.89, 1.79]
  weight = [65.4, 59.2, 63.6, 88.4, 68.7]
  
  np2_2d_again = np.array(height, weight)
  
  # Nope: TypeError: data type not understood
  </code></pre>