Dimensions on Periodic Metrics (#174)

* Extract configured dimensions from the data stream and bucket periodic instrument by them.

* Added a test and fixed sample counting.

Author: vjkoskela

src/main/java/com/arpnetworking/tsdcore/model/DefaultKey.java

@@ -18,7 +18,9 @@
 import com.arpnetworking.logback.annotations.Loggable;
 import com.google.common.base.MoreObjects;
 import com.google.common.collect.ImmutableMap;
+import com.google.common.collect.ImmutableSet;
 
+import java.util.Map;
 import java.util.Objects;
 
 /**
@@ -49,6 +51,17 @@ public String getHost() {
         return _dimensions.get(HOST_DIMENSION_KEY);
     }
 
+    @Override
+    public Key filter(final ImmutableSet<String> keys) {
+        return new DefaultKey(
+                _dimensions.entrySet()
+                        .stream()
+                        .filter(e -> keys.contains(e.getKey()))
+                        .collect(ImmutableMap.toImmutableMap(
+                                Map.Entry::getKey,
+                                Map.Entry::getValue)));
+    }
+
     @Override
     public boolean equals(final Object other) {
         if (this == other) {

src/main/java/com/arpnetworking/tsdcore/model/Key.java

@@ -16,6 +16,7 @@
 package com.arpnetworking.tsdcore.model;
 
 import com.google.common.collect.ImmutableMap;
+import com.google.common.collect.ImmutableSet;
 
 /**
  * Interface for aggregation context (e.g. slice of hyper-cube).
@@ -52,6 +53,15 @@ public interface Key {
      */
     String getHost();
 
+    /**
+     * Create a {@link Key} from this key that contains a subset of the
+     * parameters by parameter key.
+     *
+     * @param keys the parameter keys to retain in the returned {@link Key}
+     * @return instance of {@link Key} with only specified parameter keys and values
+     */
+    Key filter(ImmutableSet<String> keys);
+
     /**
      * The dimension key for the cluster attribute.
      */