diff --git a/src/main/scala/com/github/mrpowers/spark/daria/sql/udafs/ArraySum.scala b/src/main/scala/com/github/mrpowers/spark/daria/sql/udafs/ArraySum.scala
new file mode 100644
index 00000000..d28586db
--- /dev/null
+++ b/src/main/scala/com/github/mrpowers/spark/daria/sql/udafs/ArraySum.scala
@@ -0,0 +1,38 @@
+package com.github.mrpowers.spark.daria.sql.udafs
+
+import org.apache.spark.sql.Row
+import org.apache.spark.sql.expressions.{MutableAggregationBuffer, UserDefinedAggregateFunction}
+import org.apache.spark.sql.types.{ArrayType, DataType, StructField, StructType}
+
+class ArraySum(elementSchema: DataType,
+    nullable: Boolean = true) extends UserDefinedAggregateFunction {
+
+  private val schema = StructType(List(StructField("value", dataType, nullable)))
+
+  override def inputSchema: StructType = schema
+
+  override def bufferSchema: StructType = schema
+
+  override def dataType: DataType = ArrayType(elementSchema)
+
+  override def deterministic: Boolean = true
+
+  override def initialize(buffer: MutableAggregationBuffer): Unit = {
+    buffer(0) = Seq.empty[Any]
+  }
+
+  override def update(buffer: MutableAggregationBuffer, input: Row): Unit = {
+    val value = input.getAs[Seq[Any]](0)
+    if (value != null) {
+      buffer(0) = buffer.getAs[Seq[Any]](0) ++ value
+    }
+  }
+
+  override def merge(buffer1: MutableAggregationBuffer, buffer2: Row): Unit = {
+    buffer1(0) = buffer1.getAs[Seq[Any]](0) ++ buffer2.getAs[Seq[Any]](0)
+  }
+
+  override def evaluate(buffer: Row): Any = {
+    buffer.getAs[Seq[Any]](0)
+  }
+}
diff --git a/src/test/scala/com/github/mrpowers/spark/daria/sql/udafs/ArraySumTest.scala b/src/test/scala/com/github/mrpowers/spark/daria/sql/udafs/ArraySumTest.scala
new file mode 100644
index 00000000..f523650a
--- /dev/null
+++ b/src/test/scala/com/github/mrpowers/spark/daria/sql/udafs/ArraySumTest.scala
@@ -0,0 +1,44 @@
+package com.github.mrpowers.spark.daria.sql.udafs
+
+import utest._
+import com.github.mrpowers.spark.daria.sql.SparkSessionExt._
+import com.github.mrpowers.spark.daria.sql.SparkSessionTestWrapper
+import com.github.mrpowers.spark.fast.tests.DataFrameComparer
+import org.apache.spark.sql.functions._
+import org.apache.spark.sql.types._
+
+
+object ArraySumTest extends TestSuite with DataFrameComparer with SparkSessionTestWrapper {
+
+  val tests = Tests {
+
+    'arraySum - {
+      "concatenates rows of arrays" - {
+
+        val arraySum =  new ArraySum(StringType)
+        val actualDF = spark
+          .createDF(
+            List(
+              Array("snake", "rat"),
+              null,
+              Array("cat", "crazy")
+            ),
+            List(("array", ArrayType(StringType), true))
+          ).agg(arraySum(col("array")).as("array"))
+
+        val expectedDF = spark
+          .createDF(
+            List(Array("snake", "rat", "cat", "crazy")),
+            List(("array", ArrayType(StringType), true))
+          )
+
+        assertSmallDataFrameEquality(
+          actualDF,
+          expectedDF
+        )
+      }
+    }
+  }
+
+}
+