---
title: keep() function
description: keep() returns a stream of tables containing only the specified columns.
url: https://docs.influxdata.com/flux/v0/stdlib/universe/keep/
estimated_tokens: 2174
product: Flux
version: v0
---

# keep() function

-   Flux 0.7.0+
-   View InfluxDB support

`keep()` returns a stream of tables containing only the specified columns.

Columns in the group key that are not specified in the `columns` parameter or identified by the `fn` parameter are removed from the group key and dropped from output tables. `keep()` is the inverse of `drop()`.

##### Function type signature

```js
(<-tables: stream[A], ?columns: [string], ?fn: (column: string) => bool) => stream[B] where A: Record, B: Record
```

For more information, see [Function type signatures](/flux/v0/function-type-signatures/).

## Parameters

### columns

Columns to keep in output tables. Cannot be used with `fn`.

### fn

Predicate function that takes a column name as a parameter (column) and returns a boolean indicating whether or not the column should be kept in output tables. Cannot be used with `columns`.

### tables

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

## Examples

-   [Keep a list of columns](#keep-a-list-of-columns)
-   [Keep columns matching a predicate](#keep-columns-matching-a-predicate)

### Keep a list of columns

```js
import "sampledata"

sampledata.int()
    |> keep(columns: ["_time", "_value"])
```

[](#view-example-input-and-output)

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

### Keep columns matching a predicate

```js
import "sampledata"

sampledata.int()
    |> keep(fn: (column) => column =~ /^_?t/)
```

[](#view-example-input-and-output)

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 | *tag |
| --- | --- |
| 2021-01-01T00:00:00Z | t1 |
| 2021-01-01T00:00:10Z | t1 |
| 2021-01-01T00:00:20Z | t1 |
| 2021-01-01T00:00:30Z | t1 |
| 2021-01-01T00:00:40Z | t1 |
| 2021-01-01T00:00:50Z | t1 |

| _time | *tag |
| --- | --- |
| 2021-01-01T00:00:00Z | t2 |
| 2021-01-01T00:00:10Z | t2 |
| 2021-01-01T00:00:20Z | t2 |
| 2021-01-01T00:00:30Z | t2 |
| 2021-01-01T00:00:40Z | t2 |
| 2021-01-01T00:00:50Z | t2 |

#### Related

-   [drop() function](/flux/v0/stdlib/universe/drop/)

[transformations](/flux/v0/tags/transformations/)