title: Scala - diff two list of case classes by subset of fields
body: <p>Given two lists of case classes</p>
  
  <pre><code>case class Entity(field1: String, field2: String, field3: String)
  val a: Seq[Entity] = ...
  val b: Seq[Entity] = ...
  </code></pre>
  
  <p>How to find all entities in a that's not in b, based on only field1 and field2, ignoring field3? </p>
  
  <p>I've considered overriding the equals() function for the case class, also the neat trick of case class ()(ignored fields goes here) approach, but there will need to be multiple combinations of these fields needed for different use cases, e.g. diff using field1 + field2, then using field 1 + field 3, etc...</p>