title: how to get first value and last value from dataframe column in pyspark?
body: <p>I Have Dataframe,I want get first value and last value from DataFrame column.</p>
  
  <pre><code>+----+-----+--------------------+
  |test|count|             support|
  +----+-----+--------------------+
  |   A|    5| 0.23809523809523808|
  |   B|    5| 0.23809523809523808|
  |   C|    4| 0.19047619047619047|
  |   G|    2| 0.09523809523809523|
  |   K|    2| 0.09523809523809523|
  |   D|    1|0.047619047619047616|
  +----+-----+--------------------+
  </code></pre>
  
  <p>expecting output is from support column first,last value i.e <code>x=[0.23809523809523808,0.047619047619047616.]</code></p>