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docs-v2/content/flux/v0.x/stdlib/universe/map.md

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title description aliases menu weight flux/v0.x/tags related introduced
map() function The `map()` function applies a function to each record in the input tables.
/influxdb/v2.0/reference/flux/functions/transformations/map
/influxdb/v2.0/reference/flux/functions/built-in/transformations/map/
/influxdb/v2.0/reference/flux/stdlib/built-in/transformations/map/
/influxdb/cloud/reference/flux/stdlib/built-in/transformations/map/
flux_0_x_ref
name parent
map universe
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transformations
/{{< latest "influxdb" >}}/query-data/flux/conditional-logic/
/{{< latest "influxdb" >}}/query-data/flux/mathematic-operations/
/flux/v0.x/stdlib/contrib/jsternberg/rows/map/
0.7.0

The map() function applies a function to each record in the input tables. The modified records are assigned to new tables based on the group key of the input table. The output tables are the result of applying the map function to each record of the input tables.

When the output record contains a different value for the group key, the record is regrouped into the appropriate table. When the output record drops a column that was part of the group key, that column is removed from the group key.

map(fn: (r) => ({ _value: r._value * r._value }))

Parameters

{{% note %}} Make sure fn parameter names match each specified parameter. To learn why, see Match parameter names. {{% /note %}}

fn

A single argument function to apply to each record. The return value must be a record.

{{% note %}} Records evaluated in fn functions are represented by r, short for "record" or "row". {{% /note %}}

tables

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

Important notes

Preserve columns

By default, map() drops any columns that:

  1. Are not part of the input table's group key.
  2. Are not explicitly mapped in the map() function.

This often results in the _time column being dropped. To preserve the _time column and other columns that do not meet the criteria above, use the with operator to map values in the r record. The with operator updates a column if it already exists, creates a new column if it doesn't exist, and includes all existing columns in the output table.

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

Examples

{{% flux/sample-example-intro plural=true %}}

Square the value in each row

import "sampledata"

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

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

Input data

{{% flux/sample "int" %}}

{{% /flex-content %}} {{% flex-content %}}

Output data
_time tag _value
2021-01-01T00:00:00Z t1 4
2021-01-01T00:00:10Z t1 100
2021-01-01T00:00:20Z t1 49
2021-01-01T00:00:30Z t1 289
2021-01-01T00:00:40Z t1 225
2021-01-01T00:00:50Z t1 16
_time tag _value
2021-01-01T00:00:00Z t2 361
2021-01-01T00:00:10Z t2 16
2021-01-01T00:00:20Z t2 9
2021-01-01T00:00:30Z t2 361
2021-01-01T00:00:40Z t2 169
2021-01-01T00:00:50Z t2 1

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

Create a new table with new columns

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 input and output" %}} {{< flex >}} {{% flex-content %}}

Input data

{{% flux/sample "int" %}}

{{% /flex-content %}} {{% flex-content %}}

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

{{% /flex-content %}} {{< /flex >}} {{% /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.

import "sampledata"

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

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

Input data

{{% flux/sample "int" %}}

{{% /flex-content %}} {{% flex-content %}}

Output data
_time tag _value server valueFloat
2021-01-01T00:00:00Z t1 -2 server-t1 -2.0
2021-01-01T00:00:10Z t1 10 server-t1 10.0
2021-01-01T00:00:20Z t1 7 server-t1 7.0
2021-01-01T00:00:30Z t1 17 server-t1 17.0
2021-01-01T00:00:40Z t1 15 server-t1 15.0
2021-01-01T00:00:50Z t1 4 server-t1 4.0
_time tag _value server valueFloat
2021-01-01T00:00:00Z t2 19 server-t2 19.0
2021-01-01T00:00:10Z t2 4 server-t2 4.0
2021-01-01T00:00:20Z t2 -3 server-t2 -3.0
2021-01-01T00:00:30Z t2 19 server-t2 19.0
2021-01-01T00:00:40Z t2 13 server-t2 13.0
2021-01-01T00:00:50Z t2 1 server-t2 1.0

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

Troubleshooting

Map object property is not supported in a Flux table

Flux tables only support the following value types:

  • float
  • integer
  • unsigned integer
  • string
  • boolean
  • time

If map() returns a record with an unsupported type, Flux returns an error with the name of the column that attempted to use the unsupported type.

If mapping a duration value, use time() to convert it to a time value or int() to convert it to an integer. For the bytes type, use string() to convert the value to a string.

{{% note %}} For information about supporting other data types in Flux tables, see the following Github issues: