map() function

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.

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

Function type signature

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

Parameters

fn

(Required) 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
• Create a new table with new columns
• Add new columns and preserve existing columns

Square the value in each row

import "sampledata"

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

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}),
    )

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)}))