kotlin group by sum of property value in an arraylist

Question

I have an arraylist that contains list of objects like below:

[Activities(id=3116, studentID=5c1a7986c98da061141475b4, actionID=1234, actionName=hohoho, totalPoints=100),
Activities(id=3117, studentID=5c1a7986c98da061141475b4, actionID=4321, actionName=lalala, totalPoints=7),
Activities(id=3118, studentID=5c1a7986c98da061141475b4, actionID=4321, actionName=lalala, totalPoints=4),
Activities(id=3119, studentID=5c1a7986c98da061141475b4, actionID=1234, actionName=hohoho, totalPoints=10)]

Is there any kotlin functions that I can use that can sum the totalPoints based on group actionID from above? If the above arraylist is in sql instead, I can do something like SELECT actionID, SUM(totalPoints) FROM activities GROUP BY actionID, which will return

actionID     totalPoints
1234         110
4321         11

Answer 1

If you have the list of activities, then you can get the sum of totalPoints grouping by actionID as below

val result = activities
        .groupBy { it.actionID }
        .mapValues { entry -> entry.value.sumBy { it.totalPoints } }

result would be a map containing the actionID as its key and value as the sum of totalPoints for the respective actionID

Printing result would give

{1234=110, 4321=11}