Added umbrellaInterval method, which takes an Iterable of intervals and returns

a single interval spanning the entire range of input intervals.

common/src/main/java/com/metamx/druid/utils/JodaUtils.java

@@ -19,6 +19,7 @@
 
 package com.metamx.druid.utils;
 
+import com.google.common.base.Preconditions;
 import com.google.common.collect.Lists;
 import com.google.common.collect.Sets;
 import com.metamx.common.guava.Comparators;
@@ -63,6 +64,35 @@ public class JodaUtils
     return retVal;
   }
 
+  public static Interval umbrellaInterval(Iterable<Interval> intervals)
+  {
+    DateTime minStart = null;
+    DateTime maxEnd = null;
+
+    for (Interval interval : intervals) {
+      DateTime curStart = interval.getStart();
+      DateTime curEnd = interval.getEnd();
+
+      if (minStart == null || maxEnd == null) {
+        minStart = curStart;
+        maxEnd = curEnd;
+      }
+
+      if (curStart.isBefore(minStart)) {
+        minStart = curStart;
+      }
+
+      if (curEnd.isAfter(maxEnd)) {
+        maxEnd = curEnd;
+      }
+    }
+
+    if (minStart == null || maxEnd == null) {
+      throw new IllegalArgumentException("Empty list of intervals");
+    }
+    return new Interval(minStart, maxEnd);
+  }
+
   public static DateTime minDateTime(DateTime... times)
   {
     if (times == null) {

common/src/test/java/com/metamx/druid/utils/JodaUtilsTest.java

@@ -31,6 +31,40 @@ import java.util.List;
  */
 public class JodaUtilsTest
 {
+  @Test
+  public void testUmbrellaIntervalsSimple() throws Exception
+  {
+    List<Interval> intervals = Arrays.asList(
+        new Interval("2011-03-03/2011-03-04"),
+        new Interval("2011-01-01/2011-01-02"),
+        new Interval("2011-02-01/2011-02-05"),
+        new Interval("2011-02-03/2011-02-08"),
+        new Interval("2011-01-01/2011-01-03"),
+        new Interval("2011-03-01/2011-03-02"),
+        new Interval("2011-03-05/2011-03-06"),
+        new Interval("2011-02-01/2011-02-02")
+    );
+
+    Assert.assertEquals(
+        new Interval("2011-01-01/2011-03-06"),
+        JodaUtils.umbrellaInterval(intervals)
+    );
+  }
+
+  @Test
+  public void testUmbrellaIntervalsNull() throws Exception
+  {
+    List<Interval> intervals = Arrays.asList();
+    Throwable thrown = null;
+    try {
+      Interval res = JodaUtils.umbrellaInterval(intervals);
+    }
+    catch (IllegalArgumentException e) {
+      thrown = e;
+    }
+    Assert.assertNotNull("Empty list of intervals", thrown);
+  }
+
   @Test
   public void testCondenseIntervalsSimple() throws Exception
   {