title: Select same length of subarrays by evenly spacing in numpy
body: <p>I'm new to python and stackoverflow and I'm working on a project that deal with manually created arrays with different length. </p>
  
  <pre><code>path = '/home/Documents/Noise'
  files = glob.glob(path + '/*.txt')
  data_noise = []
  for file in files:
      df = pd.read_csv(file, delimiter=',', header=None)
      df = df.values
      m,n = df.shape
      df = np.reshape(df,m)
      data_noise.append(df)
  </code></pre>
  
  <p>I create a list <code>data_noise</code> to store numpy arrays, each array has different length <code>m</code>. I want to select subarrays from each array so that they have same length, say, 100. But instead of selecting the first 100 elements or the last 100 in each array, I want to evenly space and select in each array.</p>
  
  <p>For example, for a length 300 array, I need elements indexed by 0,3,6,9,... and for a length 500 array, I need elements indexed by 0,5,10,15,...</p>
  
  <p>How do I modify my code to do that?</p>