title: when use matplotlib for making graph, how can i select range?
body: <p>in case,
      import numpy as np
      import matplotlib.pyplot as plt</p>
  
  <pre><code>x = np.linspace(0, 10, 20)
  y = x**2 + 2
  </code></pre>
  
  <p>usually make graph for plt.plot(x,y)
  but i have useless part.
  I thought this to make new array and then append.</p>
  
  <pre><code>t = np.array([])
  for i in range(len(x)):
      if 4 &lt; i and i &lt; 9:
          continue
      t = np.append(t,x[i])
  
  plt.plot(t,y)
  </code></pre>
  
  <p>or
      new_x = np.array([])</p>
  
  <pre><code>for i in range(len(x)):
      if 4&lt;i and i&lt;9:
          new_x = np.delete(x,i)
  plt.plot(new_x,y)
  </code></pre>
  
  <p>So, i can remove useless parts.
  Does anybody know more good idea for working hour? I have huge datas.</p>