title: Extract words from a string column in spark dataframe
body: <p>I have a column in spark dataframe which has text.</p>
  <p>I want to extract all the words which start with a special character <code>'@'</code> and I am using <code>regexp_extract</code> from each row in that text column. If the text contains multiple words starting with <code>'@'</code> it just returns the first one.</p>
  <p>I am looking for extracting multiple words which match my pattern in Spark.</p>
  <pre><code>data_frame.withColumn(&quot;Names&quot;, regexp_extract($&quot;text&quot;,&quot;(?&lt;=^|(?&lt;=[^a-zA-Z0-9-_\.]))@([A-Za-z]+[A-Za-z0-9_]+)&quot;,1).show
  </code></pre>
  <p>Sample input: <code>@always_nidhi @YouTube no i dnt understand bt i loved the music nd their dance awesome all the song of this mve is rocking</code></p>
  <p>Sample output: <code>@always_nidhi,@YouTube</code></p>