Add difference of the first value and the last value for aggregators

Signed-off-by: Chris Larsen <[email protected]>

src/core/Aggregators.java

@@ -82,6 +82,11 @@ public enum Interpolation {
   public static final Aggregator DEV = new StdDev(
       Interpolation.LERP, "dev");
 
+  /** Aggregator that returns the difference of the first value and the 
+   * last value in the data points */
+  public static final Aggregator DIFF = new Diff(
+      Interpolation.LERP, "diff");
+
   /** Sums data points but will cause the SpanGroup to return a 0 if timestamps
    * don't line up instead of interpolating. */
   public static final Aggregator ZIMSUM = new Sum(
@@ -174,6 +179,7 @@ public enum Interpolation {
     aggregators.put("median", MEDIAN);
     aggregators.put("mult", MULTIPLY);
     aggregators.put("dev", DEV);
+    aggregators.put("diff", DIFF);
     aggregators.put("count", COUNT);
     aggregators.put("zimsum", ZIMSUM);
     aggregators.put("mimmin", MIMMIN);
@@ -526,6 +532,53 @@ public double runDouble(final Doubles values) {
 
   }
 
+  /**
+   * Difference of the first value and the last value in multi values aggregator.
+   */
+  private static final class Diff extends net.opentsdb.core.Aggregator {
+    public Diff(final Interpolation method, final String name) {
+      super(method, name);
+    }
+
+    @Override
+    public long runLong(final Longs values) {
+      long first_mean = values.nextLongValue();
+
+      if (!values.hasNextValue()) {
+        return 0;
+      }
+
+      long last_mean = 0;
+      do {
+        last_mean = values.nextLongValue();
+      } while (values.hasNextValue());
+
+      return last_mean - first_mean;
+    }
+
+    @Override
+    public double runDouble(final Doubles values) {
+      double first_mean = values.nextDoubleValue();
+      while (Double.isNaN(first_mean) && values.hasNextValue()) {
+        first_mean = values.nextDoubleValue();
+      }
+
+      if (Double.isNaN(first_mean)) {
+        return Double.NaN;
+      }
+      if (!values.hasNextValue()) {
+        return 0.;
+      }
+
+      double last_mean = 0.;
+      do {
+        last_mean = values.nextDoubleValue();
+      } while (values.hasNextValue());
+
+      return last_mean - first_mean;
+    }
+  }
+
   private static final class Count extends Aggregator {
     public Count(final Interpolation method, final String name) {
       super(method, name);

tools/check_tsd

@@ -29,7 +29,7 @@ import sys
 import time
 from optparse import OptionParser
 
-AGGREGATORS = ('avg', 'count', 'dev',
+AGGREGATORS = ('avg', 'count', 'dev', 'diff',
         'ep50r3', 'ep50r7', 'ep75r3', 'ep75r7', 'ep90r3', 'ep90r7', 'ep95r3', 'ep95r7',
         'ep99r3', 'ep99r7', 'ep999r3', 'ep999r7',
         'mimmin', 'mimmax', 'min', 'max', 'none',