---
title: group() function
description: >
  `group()` regroups input data by modifying group key of input tables.
menu:
  flux_v0_ref:
    name: group
    parent: universe
    identifier: universe/group
weight: 101
flux/v0/tags: [transformations]
introduced: 0.7.0
---

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`group()` regroups input data by modifying group key of input tables.

**Note**: Group does not guarantee sort order.
To ensure data is sorted correctly, use `sort()` after `group()`.

##### 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

List of columns to use in the grouping operation. Default is `[]`.

**Note**: When `columns` is set to an empty array, `group()` ungroups
all data merges it into a single output table.

### mode

Grouping mode. Default is `by`.

**Available modes**:
- **by**: Group by columns defined in the `columns` parameter.
- **except**: Group by all columns _except_ those in defined in the
`columns` parameter.

### tables

Input data. Default is piped-forward data (`<-`).




## Examples

- [Group by specific columns](#group-by-specific-columns)
- [Group by everything except time](#group-by-everything-except-time)
- [Ungroup data](#ungroup-data)

### Group by specific columns

```js
import "sampledata"

sampledata.int()
    |> group(columns: ["_time", "tag"])

```

{{< expand-wrapper >}}
{{% expand "View example input and output" %}}

#### Input data

| _time                | _value  | *tag |
| -------------------- | ------- | ---- |
| 2021-01-01T00:00:00Z | -2      | t1   |
| 2021-01-01T00:00:10Z | 10      | t1   |
| 2021-01-01T00:00:20Z | 7       | t1   |
| 2021-01-01T00:00:30Z | 17      | t1   |
| 2021-01-01T00:00:40Z | 15      | t1   |
| 2021-01-01T00:00:50Z | 4       | t1   |

| _time                | _value  | *tag |
| -------------------- | ------- | ---- |
| 2021-01-01T00:00:00Z | 19      | t2   |
| 2021-01-01T00:00:10Z | 4       | t2   |
| 2021-01-01T00:00:20Z | -3      | t2   |
| 2021-01-01T00:00:30Z | 19      | t2   |
| 2021-01-01T00:00:40Z | 13      | t2   |
| 2021-01-01T00:00:50Z | 1       | t2   |


#### Output data

| *_time               | _value  | *tag |
| -------------------- | ------- | ---- |
| 2021-01-01T00:00:00Z | -2      | t1   |

| *_time               | _value  | *tag |
| -------------------- | ------- | ---- |
| 2021-01-01T00:00:00Z | 19      | t2   |

| *_time               | _value  | *tag |
| -------------------- | ------- | ---- |
| 2021-01-01T00:00:10Z | 10      | t1   |

| *_time               | _value  | *tag |
| -------------------- | ------- | ---- |
| 2021-01-01T00:00:10Z | 4       | t2   |

| *_time               | _value  | *tag |
| -------------------- | ------- | ---- |
| 2021-01-01T00:00:20Z | 7       | t1   |

| *_time               | _value  | *tag |
| -------------------- | ------- | ---- |
| 2021-01-01T00:00:20Z | -3      | t2   |

| *_time               | _value  | *tag |
| -------------------- | ------- | ---- |
| 2021-01-01T00:00:30Z | 17      | t1   |

| *_time               | _value  | *tag |
| -------------------- | ------- | ---- |
| 2021-01-01T00:00:30Z | 19      | t2   |

| *_time               | _value  | *tag |
| -------------------- | ------- | ---- |
| 2021-01-01T00:00:40Z | 15      | t1   |

| *_time               | _value  | *tag |
| -------------------- | ------- | ---- |
| 2021-01-01T00:00:40Z | 13      | t2   |

| *_time               | _value  | *tag |
| -------------------- | ------- | ---- |
| 2021-01-01T00:00:50Z | 4       | t1   |

| *_time               | _value  | *tag |
| -------------------- | ------- | ---- |
| 2021-01-01T00:00:50Z | 1       | t2   |

{{% /expand %}}
{{< /expand-wrapper >}}

### Group by everything except time

```js
import "sampledata"

sampledata.int()
    |> group(columns: ["_time"], mode: "except")

```

{{< expand-wrapper >}}
{{% expand "View example input and output" %}}

#### Input data

| _time                | _value  | *tag |
| -------------------- | ------- | ---- |
| 2021-01-01T00:00:00Z | -2      | t1   |
| 2021-01-01T00:00:10Z | 10      | t1   |
| 2021-01-01T00:00:20Z | 7       | t1   |
| 2021-01-01T00:00:30Z | 17      | t1   |
| 2021-01-01T00:00:40Z | 15      | t1   |
| 2021-01-01T00:00:50Z | 4       | t1   |

| _time                | _value  | *tag |
| -------------------- | ------- | ---- |
| 2021-01-01T00:00:00Z | 19      | t2   |
| 2021-01-01T00:00:10Z | 4       | t2   |
| 2021-01-01T00:00:20Z | -3      | t2   |
| 2021-01-01T00:00:30Z | 19      | t2   |
| 2021-01-01T00:00:40Z | 13      | t2   |
| 2021-01-01T00:00:50Z | 1       | t2   |


#### Output data

| _time                | *_value | *tag |
| -------------------- | ------- | ---- |
| 2021-01-01T00:00:20Z | -3      | t2   |

| _time                | *_value | *tag |
| -------------------- | ------- | ---- |
| 2021-01-01T00:00:00Z | -2      | t1   |

| _time                | *_value | *tag |
| -------------------- | ------- | ---- |
| 2021-01-01T00:00:50Z | 1       | t2   |

| _time                | *_value | *tag |
| -------------------- | ------- | ---- |
| 2021-01-01T00:00:50Z | 4       | t1   |

| _time                | *_value | *tag |
| -------------------- | ------- | ---- |
| 2021-01-01T00:00:10Z | 4       | t2   |

| _time                | *_value | *tag |
| -------------------- | ------- | ---- |
| 2021-01-01T00:00:20Z | 7       | t1   |

| _time                | *_value | *tag |
| -------------------- | ------- | ---- |
| 2021-01-01T00:00:10Z | 10      | t1   |

| _time                | *_value | *tag |
| -------------------- | ------- | ---- |
| 2021-01-01T00:00:40Z | 13      | t2   |

| _time                | *_value | *tag |
| -------------------- | ------- | ---- |
| 2021-01-01T00:00:40Z | 15      | t1   |

| _time                | *_value | *tag |
| -------------------- | ------- | ---- |
| 2021-01-01T00:00:30Z | 17      | t1   |

| _time                | *_value | *tag |
| -------------------- | ------- | ---- |
| 2021-01-01T00:00:00Z | 19      | t2   |
| 2021-01-01T00:00:30Z | 19      | t2   |

{{% /expand %}}
{{< /expand-wrapper >}}

### Ungroup data

```js
import "sampledata"

// Merge all tables into a single table
sampledata.int()
    |> group()

```

{{< expand-wrapper >}}
{{% expand "View example input and output" %}}

#### Input data

| _time                | _value  | *tag |
| -------------------- | ------- | ---- |
| 2021-01-01T00:00:00Z | -2      | t1   |
| 2021-01-01T00:00:10Z | 10      | t1   |
| 2021-01-01T00:00:20Z | 7       | t1   |
| 2021-01-01T00:00:30Z | 17      | t1   |
| 2021-01-01T00:00:40Z | 15      | t1   |
| 2021-01-01T00:00:50Z | 4       | t1   |

| _time                | _value  | *tag |
| -------------------- | ------- | ---- |
| 2021-01-01T00:00:00Z | 19      | t2   |
| 2021-01-01T00:00:10Z | 4       | t2   |
| 2021-01-01T00:00:20Z | -3      | t2   |
| 2021-01-01T00:00:30Z | 19      | t2   |
| 2021-01-01T00:00:40Z | 13      | t2   |
| 2021-01-01T00:00:50Z | 1       | t2   |


#### Output data

| _time                | _value  | tag  |
| -------------------- | ------- | ---- |
| 2021-01-01T00:00:00Z | -2      | t1   |
| 2021-01-01T00:00:10Z | 10      | t1   |
| 2021-01-01T00:00:20Z | 7       | t1   |
| 2021-01-01T00:00:30Z | 17      | t1   |
| 2021-01-01T00:00:40Z | 15      | t1   |
| 2021-01-01T00:00:50Z | 4       | t1   |
| 2021-01-01T00:00:00Z | 19      | t2   |
| 2021-01-01T00:00:10Z | 4       | t2   |
| 2021-01-01T00:00:20Z | -3      | t2   |
| 2021-01-01T00:00:30Z | 19      | t2   |
| 2021-01-01T00:00:40Z | 13      | t2   |
| 2021-01-01T00:00:50Z | 1       | t2   |

{{% /expand %}}
{{< /expand-wrapper >}}