sum of results from for - in loop, in swift

I am playing around with Apples sample code for Health kit. They have put a for-in loop function to iterate through all the sample within the last 24hours. The code of course works great.

Using the for-in loop in swift, would it be possible to find the sum of all the values?

I have been trying but can not find the solution.

Thanks Chris

Here is the code:

for sample in results as [HKQuantitySample] {
                let joules = sample.quantity.doubleValueForUnit(HKUnit.jouleUnit())