Apache Arrow defines two formats for serializing data for interprocess communication (IPC):
a "stream" format and a "file" format, known as Feather.
interfaces for accessing record batches from input sources in those formats,
For guidance on how to use these classes, see the examples section.
factory methods instantiate the object and
take a single argument, named according to the class:
$read_next_batch(): Returns a
RecordBatch, iterating through the
Reader. If there are no further batches in the Reader, it returns
$schema: Returns a Schema (active binding)
$batches(): Returns a list of
$read_table(): Collects the reader's
RecordBatches into a Table
RecordBatchFileReader, return a particular batch
by an integer index.
RecordBatchFileReader, see how many batches
are in the file.
tf <- tempfile() on.exit(unlink(tf)) batch <- record_batch(chickwts) # This opens a connection to the file in Arrow file_obj <- FileOutputStream$create(tf) # Pass that to a RecordBatchWriter to write data conforming to a schema writer <- RecordBatchFileWriter$create(file_obj, batch$schema) writer$write(batch) # You may write additional batches to the stream, provided that they have # the same schema. # Call "close" on the writer to indicate end-of-file/stream writer$close() # Then, close the connection--closing the IPC message does not close the file file_obj$close() # Now, we have a file we can read from. Same pattern: open file connection, # then pass it to a RecordBatchReader read_file_obj <- ReadableFile$create(tf) reader <- RecordBatchFileReader$create(read_file_obj) # RecordBatchFileReader knows how many batches it has (StreamReader does not) reader$num_record_batches #>  1 # We could consume the Reader by calling $read_next_batch() until all are, # consumed, or we can call $read_table() to pull them all into a Table tab <- reader$read_table() # Call as.data.frame to turn that Table into an R data.frame df <- as.data.frame(tab) # This should be the same data we sent all.equal(df, chickwts, check.attributes = FALSE) #>  TRUE # Unlike the Writers, we don't have to close RecordBatchReaders, # but we do still need to close the file connection read_file_obj$close()