Github user cestella commented on a diff in the pull request:
https://github.com/apache/incubator-metron/pull/397#discussion_r92835008
--- Diff:
metron-platform/metron-common/src/main/java/org/apache/metron/common/dsl/functions/DataStructureFunctions.java
---
@@ -137,6 +138,105 @@ public Object apply(List<Object> args) {
}
}
+ @Stellar( namespace="HLLP"
+ , name="CARDINALITY"
+ , description="Returns HyperLogLogPlus-estimated cardinality for
this set"
+ , params = { "hyperLogLogPlus - the hllp set" }
+ , returns = "Long value representing the cardinality for this
set"
+ )
+ public static class HLLPCardinality extends BaseStellarFunction {
+
+ @Override
+ public Object apply(List<Object> args) {
+ if (args.size() < 1) {
+ throw new IllegalArgumentException("Must pass an hllp set to get
the cardinality for");
+ }
+ return ((HyperLogLogPlus) args.get(0)).cardinality();
+ }
+ }
+
+ @Stellar( namespace="HLLP"
+ , name="INIT"
+ , description="Initializes the set"
+ , params = {
+ "p (required) - the precision value for the normal
set"
--- End diff --
Are their any documents that we can link to describe the tradeoffs for
these values? I'm thinking of something like
[here](https://en.wikipedia.org/wiki/File:Bloom_filter_fp_probability.svg)
discussing the tradeoff between accuracy and size.
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