How to remove duplicates in a list

Question

From the below code, I am fetching list of records where i am getting duplicate id's..again i am passing the list to a set to avoid duplicates. Can anyone suggest a bestway to avoid duplicates in a list.

query string = select field1__c, field2__c From object1__c;
List<object1__c> obj = Database.Query(queryString);
system.debug('obj list has'+lst);
set<id> ps = new Set<id>();
for(object1__c o: obj ){
    ps.add(o.Id);
    System.debug('>>>>>>>>>>>>ps'+ ps);
}

any help is greatly appreciated.

Answer 1

Based on your example, if you just want Id field, query in a Map:

Map<Id, object1__c> mapObject = 
    new Map<Id, object1__c>([select field1__c, field2__c From object1__c]);

But Id's are never duplicates from a list.

So if you have any other list, just iterate over it and use map to collect it. Using Map.values method you can get back the list.

for(Object1__c obj: [select LookupField__c, field2__c From object1__c]) {
    mapObject.put(obj.LookupField__c);
}

List<Object1__c> lstUniqueRecords = mapObject.keySet();