Github user mmiklavc commented on a diff in the pull request:
https://github.com/apache/incubator-metron/pull/403#discussion_r95377207
--- Diff:
metron-platform/metron-common/src/main/java/org/apache/metron/common/dsl/functions/StringFunctions.java
---
@@ -284,4 +287,36 @@ private static Object fill(FillDirection direction,
Object inputObject, Object f
}
return
org.apache.commons.lang.StringUtils.rightPad(input,requiredLength,fill);
}
+
+ @Stellar( namespace="STRING"
+ , name="ENTROPY"
+ , description = "Computes the base-2 shannon entropy of a string"
+ , params = { "input - String" }
+ , returns = "The base-2 shannon entropy of the string. The unit
of this is bits."
+ )
+ public static class Entropy extends BaseStellarFunction {
+ @Override
+ public Object apply(List<Object> strings) {
+ /*
+ Shannon entropy is defined as follows:
+ \Eta(X) = - \sum(p(x_i)*log_2(p(x_i)), i=0, n-1) where x_i are
distinct characters in the string.
+ */
+ Map<Character, Integer> frequency = new HashMap<>();
+ String input = (String)strings.get(0);
--- End diff --
Super minor, but we should probably catch the no-arg provided NPE scenario
and throw new IllegalStateException showing usage to the user when they fail to
provide an arg.
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