ParentChildMapHelper

public class ParentChildMapHelper{
     public static Map<String,List<sobject>> buildGeneralisedMap(String fieldname,List<Sobject> lstsobject){
        Map<String,List<sobject>> mapIdbySobject=new Map<String,List<sobject>>();
        for(Sobject s:lstsobject){
            if (mapIdbySobject.containsKey((String)s.get(fieldname))){
                mapIdbySobject.get((String)s.get(fieldname)).add(s); //tricky part .Here map.get(key) is returning list and we are adding contacts to the list
            } else{
                List <sobject> lstsobjects = new List <sobject> (); //Initialize list as no key is found before and first time we get key 
                lstsobjects.add(s);
                mapIdbySobject.put((String)s.get(fieldname), lstsobjects);
            }  
        }
        return mapIdbySobject;
    }
}