title: Get the size/length of an array column
body: <p>I'm new in Scala programming and this is my question: How to count the number of string for each row? My Dataframe is composed of a single column of Array[String] type.</p>
  
  <pre><code>friendsDF: org.apache.spark.sql.DataFrame = [friends: array&lt;string&gt;]
  </code></pre>