docs-v2/content/flux/v0/stdlib/experimental/group.md

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---
title: experimental.group() function
description: >
`experimental.group()` introduces an `extend` mode to the existing `group()` function.
menu:
flux_v0_ref:
name: experimental.group
parent: experimental
identifier: experimental/group
weight: 101
flux/v0/tags: [transformations]
---
<!------------------------------------------------------------------------------
IMPORTANT: This page was generated from comments in the Flux source code. Any
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To make updates to this documentation, update the function comments above the
function definition in the Flux source code:
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`experimental.group()` introduces an `extend` mode to the existing `group()` function.
##### Function type signature
```js
(<-tables: stream[A], columns: [string], mode: string) => stream[A] where A: Record
```
{{% caption %}}
For more information, see [Function type signatures](/flux/v0/function-type-signatures/).
{{% /caption %}}
## Parameters
### columns
({{< req >}})
List of columns to use in the grouping operation. Default is `[]`.
### mode
({{< req >}})
Grouping mode. `extend` is the only mode available to `experimental.group()`.
#### Grouping modes
- **extend**: Appends columns defined in the `columns` parameter to group keys.
### tables
Input data. Default is piped-forward data (`<-`).
## Examples
### Add a column to the group key
```js
import "experimental"
data
|> experimental.group(columns: ["region"], mode: "extend")
```
{{< expand-wrapper >}}
{{% expand "View example input and output" %}}
#### Input data
| _time | *host | region | _value |
| -------------------- | ----- | ------- | ------- |
| 2021-01-01T00:00:00Z | host1 | east | 41 |
| 2021-01-01T00:01:00Z | host1 | east | 48 |
| 2021-01-01T00:00:00Z | host1 | west | 34 |
| 2021-01-01T00:01:00Z | host1 | west | 12 |
| _time | *host | region | _value |
| -------------------- | ----- | ------- | ------- |
| 2021-01-01T00:00:00Z | host2 | east | 56 |
| 2021-01-01T00:01:00Z | host2 | east | 72 |
| 2021-01-01T00:00:00Z | host2 | west | 43 |
| 2021-01-01T00:01:00Z | host2 | west | 22 |
#### Output data
| _time | *host | *region | _value |
| -------------------- | ----- | ------- | ------- |
| 2021-01-01T00:00:00Z | host1 | east | 41 |
| 2021-01-01T00:01:00Z | host1 | east | 48 |
| _time | *host | *region | _value |
| -------------------- | ----- | ------- | ------- |
| 2021-01-01T00:00:00Z | host1 | west | 34 |
| 2021-01-01T00:01:00Z | host1 | west | 12 |
| _time | *host | *region | _value |
| -------------------- | ----- | ------- | ------- |
| 2021-01-01T00:00:00Z | host2 | east | 56 |
| 2021-01-01T00:01:00Z | host2 | east | 72 |
| _time | *host | *region | _value |
| -------------------- | ----- | ------- | ------- |
| 2021-01-01T00:00:00Z | host2 | west | 43 |
| 2021-01-01T00:01:00Z | host2 | west | 22 |
{{% /expand %}}
{{< /expand-wrapper >}}