. Author manuscript; available in PMC: 2019 Oct 23.

Published in final edited form as: Proc ACM SIGPLAN Conf Program Lang Des Implement. 2019 Jun;2019:670–685. doi: 10.1145/3314221.3314580

Table 2.

Examples of data-trace transductions.

M = { id: ID, scalar: Float, ts: Int }
V = { scalar: Float, ts: Int }

joinFilterMap: OpStateless U(Ut, M) → U(ID, V)
Ut onItem(Ut key, M value) {
    if (location(value.id) = "window")
        emit(value.id, (value.scalar, value.ts))
}
Ut onMarker(Marker m) { }

linearInterpolation: OpKeyedOrdered O(ID, V) → O(ID, V)
Precondition: items arrive in order of increasing timestamp
V initialState() { return nil }
V onItem(V state, ID key, V value) {
    if (state == nil) then // first element
        emit(key, value)
    else // not the first element
        Float x = state.scalar
        Int dt = value.ts - state.ts
        for i = 1 … dt do
            Float y = x + i * (value.scalar - x) / dt
            emit(key, (y, state.ts + i))
    return value
}
V onMarker(V state, ID key, Marker m) { return state }

maxOfAvgPerID: OpKeyedUnordered U(ID, V) → U(ID, V)
AvgPair = { sum: Float, count: Nat }
AvgPair in(ID key, V value) { return (value.scalar, 1) }
AvgPair id() { return (0.0, 0) }
AvgPair combine(AvgPair x, AvgPair y) {
    return (x.sum + y.sum, x.count + y.count)
}
Float initialState() { return -infinity }
Float updateState(Float oldState, AvgPair agg) {
    return max(oldState, agg.sum / agg.count)
}
Ut onItem(Float lastState, ID key, V value) { }
Ut onMarker(Float newState, ID key, Marker m) {
    emit(key, (newState, m.timestamp - 1))
}