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$clone(deep = FALSE)
deep
Whether to make a deep clone.
arrow::Object
-> ScannerBuilder
Project()
ScannerBuilder$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)
deep
Whether to make a deep clone.