Adding weighted average documentation page

_aggregations/metric/index.md

@@ -44,4 +44,5 @@ OpenSearch supports the following metric aggregations:
 - [Stats]({{site.url}}{{site.baseurl}}/aggregations/metric/stats/)
 - [Sum]({{site.url}}{{site.baseurl}}/aggregations/metric/sum/)
 - [Top hits]({{site.url}}{{site.baseurl}}/aggregations/metric/top-hits/)
-- [Value count]({{site.url}}{{site.baseurl}}/aggregations/metric/value-count/)
+- [Value count]({{site.url}}{{site.baseurl}}/aggregations/metric/value-count/)
+- [Weighted average]({{site.url}}{{site.baseurl}}/aggregations/metric/weighted-average/)

_aggregations/metric/weighted-average.md

@@ -0,0 +1,96 @@
+---
+layout: default
+title: Weighted Average
+parent: Metric aggregations
+grand_parent: Aggregations
+nav_order: 150
+redirect_from:
+  - /query-dsl/aggregations/metric/weighted-average/
+---
+
+# Weighted average aggregations
+
+The `weighted average` metric is a multi-value metric aggregations that returns the weighted average value. Weighted average can be used when calculating grades for students, where various assignments and exams make-up the final grade of 100%. 
+
+A weighted average has two fields: a value and a weight.
+
+* `value`: value that the weight is applied to
+  * `missing`: (optional) to apply a default value for any missing/null value fields
+* `weight`: weight that the value is applied for
+  * `missing`: (optional) to apply a default weight for any missing/null weight fields
+
+Every value field is applied with the respective value in the `weight` field.
+
+weighted_average = ∑xw/∑w
+
+```json
+GET opensearch_dashboards_sample_data_ecommerce/_search
+{
+  "size": 0,
+  "aggs": {
+    "weighted_average_response": {
+      "weighted_avg": {
+        "value": {
+          "field": "taxless_total_price"
+        },
+        "weight": {
+          "field": "total_quantity"
+        }
+      }
+    }
+  }
+}
+```
+{% include copy-curl.html %}
+
+#### Example response
+
+```json
+{
+  "took": 2,
+  "timed_out": false,
+  "_shards": {
+    "total": 1,
+    "successful": 1,
+    "skipped": 0,
+    "failed": 0
+  },
+  "hits": {
+    "total": {
+      "value": 4675,
+      "relation": "eq"
+    },
+    "max_score": null,
+    "hits": []
+  },
+  "aggregations": {
+    "weighted_average_response": {
+      "value": 81.8645153323506
+    }
+  }
+}
+```
+
+#### Example with optional `missing` field
+
+```json
+GET opensearch_dashboards_sample_data_ecommerce/_search
+{
+  "size": 0,
+  "aggs": {
+    "weighted_average_response": {
+      "weighted_avg": {
+        "value": {
+          "field": "taxless_total_price",
+          "missing": 100
+        },
+        "weight": {
+          "field": "total_quantity",
+          "missing": 1
+        }
+      }
+    }
+  }
+}
+```
+{% include copy-curl.html %}