Merge pull request #776 from influxdata/flux/exp-aggr-pkg

Flux experimental aggregate package

content/v2.0/reference/flux/stdlib/experimental/aggregate/_index.md

@@ -0,0 +1,22 @@
+---
+title: Flux Aggregate package
+list_title: Aggregate package
+description: >
+  The Flux Aggregate package provides functions to simplify common aggregate operations.
+  Import the `experimental/aggregate` package.
+menu:
+  v2_0_ref:
+    name: Aggregate
+    parent: Experimental
+weight: 201
+v2.0/tags: [package]
+---
+
+The Flux Aggregate package provides functions to simplify common aggregate operations.
+Import the `experimental/aggregate` package:
+
+```js
+import "experimental/aggregate"
+```
+
+{{< children type="functions" show="pages" >}}

content/v2.0/reference/flux/stdlib/experimental/aggregate/rate.md

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+---
+title: aggregate.rate() function
+description: >
+  The `aggregate.rate()` function calculates the rate of change per windows of time.
+menu:
+  v2_0_ref:
+    name: aggregate.rate
+    parent: Aggregate
+weight: 301
+---
+
+The `aggregate.rate()` function calculates the rate of change per windows of time.
+
+_**Function type:** Transformation_
+
+```js
+import "experimental/query"
+
+aggregate.rate(
+  every: 1m,
+  groupColumns: ["column1", "column2"],
+  unit: 1s
+)
+```
+
+## Parameters
+
+### every
+Duration of time windows.
+
+_**Data type:** Duration_
+
+### groupColumns
+List of columns to group by. Defaults to `[]`.
+
+_**Data type:** Array of strings_
+
+### unit
+The time duration to use when calculating the rate. Defaults to `1s`.
+
+_**Data type:** Duration_
+
+## Examples
+
+```js
+import "experimental/aggregate"
+
+from(bucket: "example-bucket")
+  |> range(start: -1h)
+  |> aggregate.rate(every: 5m, unit: 1m)
+```
+
+## Function definition
+```js
+package aggregate
+
+import "experimental"
+
+rate = (tables=<-, every, groupColumns=[], unit=1s) =>
+  tables
+    |> derivative(nonNegative:true, unit:unit)
+    |> aggregateWindow(every: every, fn : (tables=<-, column) =>
+      tables
+        |> mean(column: column)
+        |> group(columns: groupColumns)
+        |> experimental.group(columns: ["_start", "_stop"], mode:"extend")
+        |> sum()
+    )
+```
+
+_**Used functions:**_  
+[aggregateWindow()](/v2.0/reference/flux/stdlib/built-in/transformations/aggregates/aggregatewindow/)  
+[derivative()](/v2.0/reference/flux/stdlib/built-in/transformations/aggregates/derivative/)  
+[experimental.group()](/v2.0/reference/flux/stdlib/experimental/group/)  
+[group()](/v2.0/reference/flux/stdlib/built-in/transformations/group/)  
+[mean()](/v2.0/reference/flux/stdlib/built-in/transformations/aggregates/mean/)  
+[sum()](/v2.0/reference/flux/stdlib/built-in/transformations/aggregates/sum/)