title: Extract certain columns of 3d numpy array
body: <p>I want to extract certain columns out of a 3d numpy array. Imagine a 3d numpy array like</p>
  
  <pre><code>[[[ 65 234 169]
    [203 191 245]
    [ 36  58 196]
    [207 208 143]
    [251 208 187]]
  
   [[ 79  69 237]
    [ 13 124  42]
    [104 165  82]
    [170 178 178]
    [ 66  42 210]]
  
   [[ 40 163 219]
    [142  37 140]
    [ 75 205 143]
    [246  30 221]
    [ 16  98 102]]]
  </code></pre>
  
  <p>If - for example - columns 2-4 should be extracted, I want to get a resulting 3d array like</p>
  
  <pre><code>[[[203 191 245]
    [ 36  58 196]
    [207 208 143]]
  
   [[ 13 124  42]
    [104 165  82]
    [170 178 178]]
  
   [[142  37 140]
    [ 75 205 143]
    [246  30 221]]]
  </code></pre>
  
  <p>I've been playing around with array indexing and slicing for a few hours, but I don't get it working.
  Could anyboday help me or?</p>
  
  <p>Thanks in advance and best regards.</p>