public List<AggregateResult> getChartData() {

   List<AggregateResult> tw = [SELECT AVG(Engagement_Delta__c) delta, Day__c FROM Engagement_Delta__c WHERE Execution_Date__c = THIS_WEEK GROUP BY Day__c];
   List<AggregateResult> lw = [SELECT AVG(Engagement_Delta__c) delta, Day__c FROM Engagement_Delta__c WHERE Execution_Date__c = LAST_WEEK GROUP BY Day__c];

   List<AggregateResult> MasterList = new List<AggregateResult>();

   MasterList.addall(tw); MasterList.addall(lw);
   return MasterList;
    }