merge()

After the accumulate phase completes, the merge() method is then used to merge all of the states generated by the accumulate method together into a final state for each group of data. If the merge() method returns null, the current values stored in the UDAF state variables are not updated.

function merge(state1,state2)
    state1[1] = state1[1] + state2[1]
    state1[2] = state1[2] + state2[2]
    return state1
end