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.
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, $ToTable(), which evaluates the
query and returns an Arrow Table.
arrow::Object -> Scanner
ToTable()Scanner$ToTable()
clone()The objects of this class are cloneable with this method.
Scanner$clone(deep = FALSE)
deepWhether to make a deep clone.
arrow::Object -> ScannerBuilder
Project()ScannerBuilder$Project(cols)
Filter()ScannerBuilder$Filter(expr)
UseThreads()ScannerBuilder$UseThreads(threads = option_use_threads())
Finish()ScannerBuilder$Finish()
clone()The objects of this class are cloneable with this method.
ScannerBuilder$clone(deep = FALSE)
deepWhether to make a deep clone.