How to aggregate values in a list by specific elements

I'm using the salesforce (apex) language, so I'm posting in the java group since apex is a derivative of the java language.  I hope someone can help.

I have a batch program I'm working on that contains a list of sobjects that haven't been inserted and I need to loop over the list and find the elements in the list that have the same fund and contact and aggregate several fields. Once I have the new list, then I do the insert.

I've been struggling on how to correctly loop over my list to find the same elements by fund and contact and then do the aggregation of the currency fields? The first issue is that the list isn't sorted so how do I find the correct elements to aggregate the values?

This is the pattern I was tyring, but it doesn't work.

List<My_SObject__c> listToInsert = new List<My_SObject__c>();
String fundName = '';
Id contactId = null;
for(My_SObject__c obj : tempList) {
    if(obj.FundName__c = fundName && obj.Contact__c == contactId) {
        obj.MyCurrencyFieldToAggregate__c += obj.MyCurrencyFieldToAggregate__c;
        listToInsert.add(obj);
    }
 fundName = obj.FundName__c;
 contactId = obj.Contact__c;
}

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Any help is appreciated.
Thanks.
-Dman100-Software ConsultantAsked:
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CEHJConnect With a Mentor Commented:
The aggregation is occurring as a result of the wrapper class implementing equals using the key criteria of fund and contact. It ignores any other attributes. Equality is met by fund and contact matching
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CEHJCommented:
You could aggregate by using Set operations with a wrapper class. Better to demonstrate: run the following and note the aggregation by 'fund' and 'contact'
Sales.java
SalesWrapper.java
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-Dman100-Software ConsultantAuthor Commented:
Hi CEHJ,

Thanks for the example, I'm looking at the code and trying to decipher what it is doing.  Can you explain the aggregation portion?  Is the aggregation occurring in the SalesWrapper class in the two overridden methods?

Thanks for your help!  I very much appreciate it!
Regards.
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