title: Setting scatter points transparency from data array in matplotlib plot
body: <p>I am plotting data with matplotlib, I have obtained a scatter plot from two numpy arrays:</p>
  
  <p>ax1.scatter(p_100,tgw_e100,color='m',s=10,label="time 0")</p>
  
  <p>I would like to add information about the eccentricity of each point.
  For this purpose I have a third array of the same length of <code>p_100</code> and <code>tgw_e100</code>, <code>ecc_100</code> whose items range from 0 to 1.</p>
  
  <p>So I would like to set the transparency of my points using data from <code>ecc_100</code> creating some sort of shade scale.</p>
  
  <p>I have tried this:</p>
  
  <pre><code>ax1.scatter(p_100,tgw_e100,color='m',alpha = ecc_100,s=10,label="time 0")
  </code></pre>
  
  <p>But I got this error:</p>
  
  <pre><code>ValueError: setting an array element with a sequence.
  </code></pre>