How to reproduce a unique list based on a field value

Question

Lets say I have a list of a sObject with several records which have a some same values in a field/column. What is the fastest way to reproduce a new list with only unique values for this list.

Record List
ID Name AGE
0  A    18
1  B    19
2  C    19
3  D    21
4  E    21

Result List (based on age)
ID Name AGE
0  A    18
1  B    19
3  D    21

Answer 1

Whenever you need a unique anything, you need a Set or a Map, depending on the circumstances. For example, unique values by Age:

Map<Decimal, SObjType> uniqueAges = new map<Decimal, SObjType>();
for(SObjType record: recordList) {
  if(!uniqueAges.containsKey(record.Age__c)) {
      uniqueAges.put(record.Age__c, record));
  }
}
SObjType[] uniqueList = uniqueAges.values();

This is obviously more pseudo-code, but you should be able to work it out from here.

---

More generically, you can write a method for this:

public static SObject[] getUniqueValues(SObject[] records, SObjectField field) {
    Map<Object, SObject> uniqueValues = new Map<Object, SObject>();
    for(SObject record: records) {
        if(!uniqueValues.containsKey(record.get(field))) {
            uniqueValues.put(record.get(field), record);
        }
    }
    return uniqueValues.values();
}