filter() function

The filter() function filters data based on conditions defined in a predicate function (fn). The output tables have the same schema as the corresponding input tables.

Function type: Transformation
Output data type: Record

filter(
  fn: (r) => r._measurement == "cpu",
  onEmpty: "drop"
)

Parameters

fn

A single argument predicate function that evaluates true or false. Records are passed to the function. Those that evaluate to true are included in the output tables. Records that evaluate to null or false are not included in the output tables.

Data type: Function

onEmpty

Defines the behavior for empty tables. Potential values are keep and drop. Defaults to drop.

Data type: String

drop

Tables without rows are dropped.

keep

Tables without rows are output to the next transformation.

Examples

Filter based on 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"
  )

Filter out null values

from(bucket:"example-bucket")
  |> range(start:-1h)
  |> filter(fn: (r) => exists r._value )

Filter values based on thresholds

from(bucket:"example-bucket")
  |> range(start:-1h)
  |> filter(fn: (r) => r._value > 50.0 and r._value < 65.0 )

Keep empty tables when filtering

from(bucket: "example-bucket")
  |> range(start: -1h)
  |> filter(fn: (r) => r._measurement == "events" and r._field == "open")
  |> filter(fn: (r) => r.doorId =~ /^2.*/, onEmpty: "keep")