filter() function

filter() filters data based on conditions defined in a predicate function (fn).

Output tables have the same schema as the corresponding input tables.

Function type signature

(<-tables: stream[A], fn: (r: A) => bool, ?onEmpty: string) => stream[A] where A: Record

Parameters

fn

(Required) Single argument predicate function that evaluates true or false.

Records representing each row are passed to the function as r. Records that evaluate to true are included in output tables. Records that evaluate to null or false are excluded from output tables.

onEmpty

Action to take with empty tables. Default is drop.

Supported values:

• keep: Keep empty tables.
• drop: Drop empty tables.

tables

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

Examples

• Filter based on InfluxDB measurement, field, and tag
• Keep empty tables when filtering
• Filter values based on thresholds

Filter based on InfluxDB measurement, field, and tag

from(bucket: "example-bucket")
    |> range(start: -1h)
    |> filter(
        fn: (r) => r._measurement == "cpu" and r._field == "usage_system" and r.cpu == "cpu-total",
    )

Keep empty tables when filtering

import "sampledata"
import "experimental/table"

sampledata.int()
    |> filter(fn: (r) => r._value > 18, onEmpty: "keep")

Filter values based on thresholds

import "sampledata"

sampledata.int()
    |> filter(fn: (r) => r._value > 0 and r._value < 10)