diff --git a/time-series/join/index.js b/time-series/join/index.js
index 3aa8482..4aff5df 100644
--- a/time-series/join/index.js
+++ b/time-series/join/index.js
@@ -1,5 +1,6 @@
 /* @flow */
 import type { TimeSeries, TimeSeriesPoint } from 'ikeru/time-series'
+import { initialize, next } from '../tournament-tree'
 
 export default function<Data>(
   timeSeriesList: Array<TimeSeries<Data>>,
@@ -9,7 +10,23 @@ export default function<Data>(
     return []
   }
 
-  return timeSeriesList[0].map(({ time }, i) =>
-    combine(time.valueOf(), timeSeriesList.map(timeSeries => timeSeries[i]))
-  )
+  const getTime = item => item.time
+
+  let tournamentTree = initialize(timeSeriesList, getTime)
+  const groups = []
+  let currentGroup = []
+
+  while (tournamentTree.value) {
+    if (currentGroup[0] && tournamentTree.value.time !== currentGroup[0].time) {
+      groups.push(currentGroup)
+      currentGroup = []
+    }
+
+    currentGroup.push(tournamentTree.value)
+    tournamentTree = next(tournamentTree, getTime)
+  }
+
+  groups.push(currentGroup)
+
+  return groups.map(group => combine(group[0].time.valueOf(), group))
 }
diff --git a/time-series/join/index.test.js b/time-series/join/index.test.js
index e53bdda..5d2e51c 100644
--- a/time-series/join/index.test.js
+++ b/time-series/join/index.test.js
@@ -1,29 +1,31 @@
 /* @flow */
 import test from 'ava'
+import { sumBy } from 'lodash'
 import { join } from 'ikeru/time-series'
 
 test('combining multiple time series by time', t => {
   const series1 = [
     { time: Date.parse('2019-01-01'), value: 1 },
     { time: Date.parse('2019-01-02'), value: 2 },
-    { time: Date.parse('2019-01-03'), value: 3 }
+    { time: Date.parse('2019-01-03'), value: 3 },
+    { time: Date.parse('2019-01-04'), value: 4 }
   ]
 
   const series2 = [
-    { time: Date.parse('2019-01-01'), value: 4 },
-    { time: Date.parse('2019-01-02'), value: 5 },
-    { time: Date.parse('2019-01-03'), value: 6 }
+    { time: Date.parse('2019-01-02'), value: 2 },
+    { time: Date.parse('2019-01-03'), value: 3 }
   ]
 
   t.deepEqual(
-    join([series1, series2], (time, [p1, p2]) => ({
+    join([series1, series2], (time, points) => ({
       time,
-      value: p1.value + p2.value
+      value: sumBy(points, 'value')
     })),
     [
-      { time: Date.parse('2019-01-01'), value: 5 },
-      { time: Date.parse('2019-01-02'), value: 7 },
-      { time: Date.parse('2019-01-03'), value: 9 }
+      { time: Date.parse('2019-01-01'), value: 1 },
+      { time: Date.parse('2019-01-02'), value: 4 },
+      { time: Date.parse('2019-01-03'), value: 6 },
+      { time: Date.parse('2019-01-04'), value: 4 }
     ]
   )
 })
diff --git a/time-series/merge/index.js b/time-series/merge/index.js
index 6014188..37f02df 100644
--- a/time-series/merge/index.js
+++ b/time-series/merge/index.js
@@ -1,6 +1,6 @@
 /* @flow */
 import type { TimeSeries } from 'ikeru/time-series'
-import { initialize, next } from './tournament-tree'
+import { initialize, next } from '../tournament-tree'
 
 export default function<Data>(
   ...timeSeriesList: Array<TimeSeries<Data>>
diff --git a/time-series/merge/tournament-tree/index.js b/time-series/tournament-tree/index.js
similarity index 100%
rename from time-series/merge/tournament-tree/index.js
rename to time-series/tournament-tree/index.js
diff --git a/time-series/merge/tournament-tree/initialize.js b/time-series/tournament-tree/initialize.js
similarity index 100%
rename from time-series/merge/tournament-tree/initialize.js
rename to time-series/tournament-tree/initialize.js
diff --git a/time-series/merge/tournament-tree/next.js b/time-series/tournament-tree/next.js
similarity index 100%
rename from time-series/merge/tournament-tree/next.js
rename to time-series/tournament-tree/next.js
diff --git a/time-series/merge/tournament-tree/tournament-tree.js b/time-series/tournament-tree/tournament-tree.js
similarity index 100%
rename from time-series/merge/tournament-tree/tournament-tree.js
rename to time-series/tournament-tree/tournament-tree.js