keep() function

keep() returns a stream of tables containing only the specified columns.

Columns in the group key that are not specified in the columns parameter or identified by the fn parameter are removed from the group key and dropped from output tables. keep() is the inverse of drop().

Function type signature

(<-tables: stream[A], ?columns: [string], ?fn: (column: string) => bool) => stream[B] where A: Record, B: Record

Parameters

columns

Columns to keep in output tables. Cannot be used with fn.

fn

Predicate function that takes a column name as a parameter (column) and returns a boolean indicating whether or not the column should be kept in output tables. Cannot be used with columns.

tables

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

Examples

• Keep a list of columns
• Keep columns matching a predicate

Keep a list of columns

import "sampledata"

sampledata.int()
    |> keep(columns: ["_time", "_value"])

Keep columns matching a predicate

import "sampledata"

sampledata.int()
    |> keep(fn: (column) => column =~ /^_?t/)