code: function(submission) {
    return _.flatten(submission.formFields.map(function(field) {
      return field.fieldValues.filter(hasGroupId);
    }).map(function(fieldValue) {
      return fieldValue.map(extractGroupId);
    }));
  }
docs: Returns all the `groupId` values for the passed-in submission.
  
  A submission can have multiple fields, and each field can have
  multiple fieldValues.