---
title: map() function
description: >
  `map()` iterates over and applies a function to input rows.
menu:
  flux_v0_ref:
    name: map
    parent: universe
    identifier: universe/map
weight: 101
flux/v0/tags: [transformations]
introduced: 0.7.0
---

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`map()` iterates over and applies a function to input rows.

Each input row is passed to the `fn` as a record, `r`.
Each `r` property represents a column key-value pair.
Output values must be of the following supported column types:

- float
- integer
- unsigned integer
- string
- boolean
- time

### Output data
Output tables are the result of applying the map function (`fn`) to each
record of the input tables. Output records are assigned to new tables based
on the group key of the input stream.
If the output record contains a different value for a group key column, the
record is regrouped into the appropriate table.
If the output record drops a group key column, that column is removed from
the group key.

#### Preserve columns
`map()` drops any columns that are not mapped explicitly by column label or
implicitly using the `with` operator in the `fn` function.
The `with` operator updates a record property if it already exists, creates
a new record property if it doesn’t exist, and includes all existing
properties in the output record.

```no_run
data
    |> map(fn: (r) => ({ r with newColumn: r._value * 2 }))
```

##### Function type signature

```js
(<-tables: stream[A], fn: (r: A) => B, ?mergeKey: bool) => stream[B]
```

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

## Parameters

### fn
({{< req >}})
Single argument function to apply to each record.
The return value must be a record.



### mergeKey

_(Deprecated)_ Merge group keys of mapped records. Default is `false`.



### tables

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




## Examples

- [Square the value in each row](#square-the-value-in-each-row)
- [Create a new table with new columns](#create-a-new-table-with-new-columns)
- [Add new columns and preserve existing columns](#add-new-columns-and-preserve-existing-columns)

### Square the value in each row

```js
import "sampledata"

sampledata.int()
    |> map(fn: (r) => ({r with _value: r._value * r._value}))

```

{{< 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 | 4       | t1   |
| 2021-01-01T00:00:10Z | 100     | t1   |
| 2021-01-01T00:00:20Z | 49      | t1   |
| 2021-01-01T00:00:30Z | 289     | t1   |
| 2021-01-01T00:00:40Z | 225     | t1   |
| 2021-01-01T00:00:50Z | 16      | t1   |

| _time                | _value  | *tag |
| -------------------- | ------- | ---- |
| 2021-01-01T00:00:00Z | 361     | t2   |
| 2021-01-01T00:00:10Z | 16      | t2   |
| 2021-01-01T00:00:20Z | 9       | t2   |
| 2021-01-01T00:00:30Z | 361     | t2   |
| 2021-01-01T00:00:40Z | 169     | t2   |
| 2021-01-01T00:00:50Z | 1       | t2   |

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

### Create a new table with new columns

```js
import "sampledata"

sampledata.int()
    |> map(
        fn: (r) => ({time: r._time, source: r.tag, alert: if r._value > 10 then true else false}),
    )

```

{{< 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                 | source  | alert  |
| -------------------- | ------- | ------ |
| 2021-01-01T00:00:00Z | t1      | false  |
| 2021-01-01T00:00:10Z | t1      | false  |
| 2021-01-01T00:00:20Z | t1      | false  |
| 2021-01-01T00:00:30Z | t1      | true   |
| 2021-01-01T00:00:40Z | t1      | true   |
| 2021-01-01T00:00:50Z | t1      | false  |
| 2021-01-01T00:00:00Z | t2      | true   |
| 2021-01-01T00:00:10Z | t2      | false  |
| 2021-01-01T00:00:20Z | t2      | false  |
| 2021-01-01T00:00:30Z | t2      | true   |
| 2021-01-01T00:00:40Z | t2      | true   |
| 2021-01-01T00:00:50Z | t2      | false  |

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

### Add new columns and preserve existing columns

Use the `with` operator on the `r` record to preserve columns not directly
operated on by the map operation.

```js
import "sampledata"

sampledata.int()
    |> map(fn: (r) => ({r with server: "server-${r.tag}", valueFloat: float(v: r._value)}))

```

{{< 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  | server    | *tag | valueFloat  |
| -------------------- | ------- | --------- | ---- | ----------- |
| 2021-01-01T00:00:00Z | -2      | server-t1 | t1   | -2          |
| 2021-01-01T00:00:10Z | 10      | server-t1 | t1   | 10          |
| 2021-01-01T00:00:20Z | 7       | server-t1 | t1   | 7           |
| 2021-01-01T00:00:30Z | 17      | server-t1 | t1   | 17          |
| 2021-01-01T00:00:40Z | 15      | server-t1 | t1   | 15          |
| 2021-01-01T00:00:50Z | 4       | server-t1 | t1   | 4           |

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

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