---
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]
---

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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 >}}