Scan the contents of a dataset

Source: R/dataset.R

A Scanner iterates over a Dataset's data fragments and returns data according to given row filtering and column projection. Use a ScannerBuilder, from a Dataset's $NewScan() method, to construct one.

Methods

ScannerBuilder has the following methods:

  • $Project(cols): Indicate that the scan should only return columns given by cols, a character vector of column names

  • $Filter(expr): Filter rows by an Expression.

  • $UseThreads(threads): logical: should the scan use multithreading? The method's default input is TRUE, but you must call the method to enable multithreading because the scanner default is FALSE.

  • $schema: Active binding, returns the Schema of the Dataset

  • $Finish(): Returns a Scanner

Scanner currently has a single method, $ToTable(), which evaluates the query and returns an Arrow Table.

Super class

arrow::Object -> Scanner

Methods

Public methods

Inherited methods

Method ToTable()

Usage

Scanner$ToTable()

Method clone()

The objects of this class are cloneable with this method.

Usage

Scanner$clone(deep = FALSE)

Arguments

deep

Whether to make a deep clone.

Super class

arrow::Object -> ScannerBuilder

Methods

Public methods

Inherited methods

Method Project()

Usage

ScannerBuilder$Project(cols)

Method Filter()

Usage

ScannerBuilder$Filter(expr)

Method UseThreads()

Usage

ScannerBuilder$UseThreads(threads = option_use_threads())

Method Finish()

Usage

ScannerBuilder$Finish()

Method clone()

The objects of this class are cloneable with this method.

Usage

ScannerBuilder$clone(deep = FALSE)

Arguments

deep

Whether to make a deep clone.