Parallel Algorithm for Data Averaging
The role of three values $V_1, V_2$ and $V_3$ isn't clear for me, but anyway:


Step 1. Sort the original list in parallel by key $K$ - you'll get a list of records $(K, V_1, V_2, V_2)$, where all the records with the same key are stored together in "buckets".
Step 2. Process each bucket concurrently, calculating all the averages.


There are many parallel sorting algorithms, you can choose one depending on your computational model.