Github user mmiklavc commented on a diff in the pull request:
https://github.com/apache/metron/pull/899#discussion_r161912600
--- Diff:
metron-stellar/stellar-common/src/main/java/org/apache/metron/stellar/dsl/functions/MathFunctions.java
---
@@ -220,4 +219,156 @@ public Object apply(List<Object> args) {
}
}
}
+
+ @Stellar(namespace = "BOYERMOORE"
+ , name = "ADD"
+ , description = "Adds value to a Boyer-Moore list.
[Boyer-Moore](https://en.wikipedia.org/wiki/Boyer%E2%80%93Moore_majority_vote_algorithm)"
+ , params = {
+ "state - state holder for list of values. If null, add will
initialize a new state value.",
+ "value(s) - single object or list of values to add to the state
object."
+ }
+ , returns = "Current state of the Boyer-Moore algorithm representing
the current value that"
+ + "holds a plurality across all values added thus far."
+ )
+ public static class BoyerMooreAdd extends BaseStellarFunction {
+
+ @Override
+ public Object apply(List<Object> args) {
+ if (args.size() < 2) {
+ throw new IllegalArgumentException(
+ "Must pass an initial state (may be null) and at least one
value to add to the list");
+ } else {
+ BoyerMooreState state = ConversionUtils.convert(args.get(0),
BoyerMooreState.class);
+ if (state == null) {
+ state = new BoyerMooreState();
+ }
+ Object secondArg = args.get(1);
+ if (secondArg instanceof List) {
+ state.addAll((List) secondArg);
+ } else {
+ state.add(secondArg);
+ }
+ return state;
+ }
+ }
+ }
+
+ public static class BoyerMooreState {
+ private Long counter;
+ private Object m;
+
+ public BoyerMooreState() {
+ counter = 0L;
+ }
+
+ public BoyerMooreState(Optional<List<BoyerMooreState>> previousStates,
Optional<BoyerMooreState> currentState) {
+ this();
+ currentState.ifPresent(boyerMooreState -> {
+ m = boyerMooreState.getPlurality();
+ counter = boyerMooreState.getCounter();
+ });
+ for (BoyerMooreState state : previousStates.orElse(new
ArrayList<>())) {
+ Object plurality = state.getPlurality();
+ Long pluralityCount = state.getCounter();
+ add(plurality, pluralityCount);
+ }
+ }
+
+ public Object add(Object item) {
+ if (item != null) {
+ if (counter == 0) {
+ m = item;
+ counter = 1L;
+ } else if (item.equals(m)) {
+ counter++;
+ } else {
+ counter--;
+ }
+ }
+ return m;
+ }
+
+ public Object add(Object item, Long counter) {
+ if (item != null) {
+ if (this.counter == 0) {
+ m = item;
+ this.counter = counter;
--- End diff --
It's true, I make no effort to massage data types here - if you want to
interpret a 1 as a string "1", then they will be considered distinct. I didn't
have a suitable mechanism for determining types. I thought it was reasonable
for a user to be able to make that type cast as part of their Stellar
expression building, but I'm certainly open to suggestions.
---
