Why readers?

Readers iterate records from a dataset in storage and load the data into DataVec. The usefulness of readers beyond individual entries in a dataset includes: what if you wanted to train a text generator on a corpus? Or programmatically compose two entries together to form a new record? Reader implementations are useful for complex file types or distributed storage mechanisms.

Readers return Writable classes that describe each column in a Record. These classes are used to convert each record to a tensor/ND-Array format.

Usage

Each reader implementation extends BaseRecordReader and provides a simple API for selecting the next record in a dataset, acting similarly to iterators.

Useful methods include:

• next: Return a batch of Writable.
• nextRecord: Return a single Record, optionally with RecordMetaData.
• reset: Reset the underlying iterator.
• hasNext: Iterator method to determine if another record is available.

Listeners

You can hook a custom RecordListener to a record reader for debugging or visualization purposes. Pass your custom listener to the addListener base method immediately after initializing your class.

Types of readers

initialize

public void initialize(InputSplit split) throws IOException, InterruptedException 

RecordReader for each pipeline. Individual record is a concatenation of the two collections.Create a recordreader that takes recordreaders and iterates over them and concatenates themhasNext would be the & of all the recordreadersconcatenation would be next & addAll on the collectionreturn one record

ConcatenatingRecordReader

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Combine multiple readers into a single reader. Records are read sequentially - thus if the first reader has100 records, and the second reader has 200 records, ConcatenatingRecordReader will have 300 records.

FileRecordReader

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File reader/writer

getCurrentLabel

public int getCurrentLabel() 

Return the current label.The index of the current file’s parent directoryin the label list

• return The index of the current file’s parent directory

LineRecordReader

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Reads files line by line

CollectionRecordReader

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Collection record reader.Mainly used for testing.

CollectionSequenceRecordReader

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Collection record reader for sequences.Mainly used for testing.

initialize

public void initialize(InputSplit split) throws IOException, InterruptedException 

• param records Collection of sequences. For example, List> where the inner two listsare a sequence, and the outer list/collection is a list of sequences

ListStringRecordReader

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Iterates through a list of strings return a record.

initialize

public void initialize(InputSplit split) throws IOException, InterruptedException 

Called once at initialization.

• param split the split that defines the range of records to read
• throws IOException
• throws InterruptedException

initialize

public void initialize(Configuration conf, InputSplit split) throws IOException, InterruptedException 

Called once at initialization.

• param conf a configuration for initialization
• param split the split that defines the range of records to read
• throws IOException
• throws InterruptedException

hasNext

public boolean hasNext() 

Get the next record

• return The list of next record

reset

public void reset() 

List of label strings

• return

nextRecord

public Record nextRecord() 

Load the record from the given DataInputStreamUnlike {- link #next()} the internal state of the RecordReader is not modifiedImplementations of this method should not close the DataInputStream

• param uri
• param dataInputStream
• throws IOException if error occurs during reading from the input stream

close

public void close() throws IOException 

Closes this stream and releases any system resources associatedwith it. If the stream is already closed then invoking thismethod has no effect.

As noted in {- link AutoCloseable#close()}, cases where theclose may fail require careful attention. It is strongly advisedto relinquish the underlying resources and to internallymark the {- code Closeable} as closed, prior to throwingthe {- code IOException}.

• throws IOException if an I/O error occurs

setConf

public void setConf(Configuration conf) 

Set the configuration to be used by this object.

• param conf

getConf

public Configuration getConf() 

Return the configuration used by this object.

CSVRecordReader

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Simple csv record reader.

initialize

public void initialize(Configuration conf, InputSplit split) throws IOException, InterruptedException 

Skip first n lines

• param skipNumLines the number of lines to skip

CSVRegexRecordReader

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A CSVRecordReader that can spliteach column into additional columns using regexs.

CSVSequenceRecordReader

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CSV Sequence Record ReaderThis reader is intended to read sequences of data in CSV format, whereeach sequence is defined in its own file (and there are multiple files)Each line in the file represents one time step

CSVVariableSlidingWindowRecordReader

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A sliding window of variable size across an entire CSV.

In practice the sliding window size starts at 1, then linearly increase to maxLinesPer sequence, thenlinearly decrease back to 1.

initialize

public void initialize(Configuration conf, InputSplit split) throws IOException, InterruptedException 

No-arg constructor with the default number of lines per sequence (10)

LibSvmRecordReader

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Record reader for libsvm format, which is closelyrelated to SVMLight format. Similar to scikit-learnwe use a single reader for both formats, so this classis a subclass of SVMLightRecordReader.

Further details on the format can be found at

• http://svmlight.joachims.org/
• http://www.csie.ntu.edu.tw/~cjlin/libsvmtools/datasets/multilabel.html
• http://scikit-learn.org/stable/modules/generated/sklearn.datasets.load_svmlight_file.html

MatlabRecordReader

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Matlab record reader

SVMLightRecordReader

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Record reader for SVMLight format, which can generallybe described as

LABEL INDEX:VALUE INDEX:VALUE …

SVMLight format is well-suited to sparse data (e.g.,bag-of-words) because it omits all features with valuezero.

We support an “extended” version that allows for multipletargets (or labels) separated by a comma, as follows:

LABEL1,LABEL2,… INDEX:VALUE INDEX:VALUE …

This can be used to represent either multitask problems ormultilabel problems with sparse binary labels (controlledvia the “MULTILABEL” configuration option).

Like scikit-learn, we support both zero-based and one-based indexing.

Further details on the format can be found at

• http://svmlight.joachims.org/
• http://www.csie.ntu.edu.tw/~cjlin/libsvmtools/datasets/multilabel.html
• http://scikit-learn.org/stable/modules/generated/sklearn.datasets.load_svmlight_file.html

initialize

public void initialize(Configuration conf, InputSplit split) throws IOException, InterruptedException 

Must be called before attempting to read records.

• param conf DataVec configuration
• param split FileSplit
• throws IOException
• throws InterruptedException

setConf

public void setConf(Configuration conf) 

Set configuration.

• param conf DataVec configuration
• throws IOException
• throws InterruptedException

hasNext

public boolean hasNext() 

Helper function to help detect lines that arecommented out. May read ahead and cache a line.

• return

nextRecord

public Record nextRecord() 

Return next record as list of Writables.

• return

RegexLineRecordReader

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RegexLineRecordReader: Read a file, one line at a time, and split it into fields using a regex.To load an entire file using a

Example: Data in format “2016-01-01 23:59:59.001 1 DEBUG First entry message!”using regex String “(\d{4}-\d{2}-\d{2} \d{2}:\d{2}:\d{2}.\d{3}) (\d+) ([A-Z]+) (.)”would be split into 4 Text writables: [“2016-01-01 23:59:59.001”, “1”, “DEBUG”, “First entry message!”]

RegexSequenceRecordReader

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RegexSequenceRecordReader: Read an entire file (as a sequence), one line at a time andsplit each line into fields using a regex.

Example: Data in format “2016-01-01 23:59:59.001 1 DEBUG First entry message!”using regex String “(\d{4}-\d{2}-\d{2} \d{2}:\d{2}:\d{2}.\d{3}) (\d+) ([A-Z]+) (.)”would be split into 4 Text writables: [“2016-01-01 23:59:59.001”, “1”, “DEBUG”, “First entry message!”]

lines that don’t match the provided regex can result in an exception (FailOnInvalid), can be skipped silently (SkipInvalid),or skip invalid but log a warning (SkipInvalidWithWarning)

TransformProcessRecordReader

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to have a transform process applied before being returned.

initialize

public void initialize(InputSplit split) throws IOException, InterruptedException 

Called once at initialization.

• param split the split that defines the range of records to read
• throws IOException
• throws InterruptedException

initialize

public void initialize(Configuration conf, InputSplit split) throws IOException, InterruptedException 

Called once at initialization.

• param conf a configuration for initialization
• param split the split that defines the range of records to read
• throws IOException
• throws InterruptedException

hasNext

public boolean hasNext() 

Get the next record

• return

reset

public void reset() 

List of label strings

• return

nextRecord

public Record nextRecord() 

Load the record from the given DataInputStreamUnlike {- link #next()} the internal state of the RecordReader is not modifiedImplementations of this method should not close the DataInputStream

• param uri
• param dataInputStream
• throws IOException if error occurs during reading from the input stream

loadFromMetaData

public Record loadFromMetaData(RecordMetaData recordMetaData) throws IOException 

Load a single record from the given {- link RecordMetaData} instanceNote: that for data that isn’t splittable (i.e., text data that needs to be scanned/split), it is more efficient toload multiple records at once using {- link #loadFromMetaData(List)}

• param recordMetaData Metadata for the record that we want to load from
• return Single record for the given RecordMetaData instance
• throws IOException If I/O error occurs during loading

setListeners

public void setListeners(RecordListener... listeners) 

Load multiple records from the given a list of {- link RecordMetaData} instances

• param recordMetaDatas Metadata for the records that we want to load from
• return Multiple records for the given RecordMetaData instances
• throws IOException If I/O error occurs during loading

setListeners

public void setListeners(Collection<RecordListener> listeners) 

Set the record listeners for this record reader.

• param listeners

close

public void close() throws IOException 

Closes this stream and releases any system resources associatedwith it. If the stream is already closed then invoking thismethod has no effect.

As noted in {- link AutoCloseable#close()}, cases where theclose may fail require careful attention. It is strongly advisedto relinquish the underlying resources and to internallymark the {- code Closeable} as closed, prior to throwingthe {- code IOException}.

• throws IOException if an I/O error occurs

setConf

public void setConf(Configuration conf) 

Set the configuration to be used by this object.

• param conf

getConf

public Configuration getConf() 

Return the configuration used by this object.

TransformProcessSequenceRecordReader

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to be transformed before being returned.

setConf

public void setConf(Configuration conf) 

Set the configuration to be used by this object.

• param conf

getConf

public Configuration getConf() 

Return the configuration used by this object.

batchesSupported

public boolean batchesSupported() 

Returns a sequence record.

• return a sequence of records

nextSequence

public SequenceRecord nextSequence() 

Load a sequence record from the given DataInputStreamUnlike {- link #next()} the internal state of the RecordReader is not modifiedImplementations of this method should not close the DataInputStream

• param uri
• param dataInputStream
• throws IOException if error occurs during reading from the input stream

loadSequenceFromMetaData

public SequenceRecord loadSequenceFromMetaData(RecordMetaData recordMetaData) throws IOException 

Load a single sequence record from the given {- link RecordMetaData} instanceNote: that for data that isn’t splittable (i.e., text data that needs to be scanned/split), it is more efficient toload multiple records at once using {- link #loadSequenceFromMetaData(List)}

• param recordMetaData Metadata for the sequence record that we want to load from
• return Single sequence record for the given RecordMetaData instance
• throws IOException If I/O error occurs during loading

initialize

public void initialize(InputSplit split) throws IOException, InterruptedException 

Load multiple sequence records from the given a list of {- link RecordMetaData} instances

• param recordMetaDatas Metadata for the records that we want to load from
• return Multiple sequence record for the given RecordMetaData instances
• throws IOException If I/O error occurs during loading

initialize

public void initialize(Configuration conf, InputSplit split) throws IOException, InterruptedException 

Called once at initialization.

• param conf a configuration for initialization
• param split the split that defines the range of records to read
• throws IOException
• throws InterruptedException

hasNext

public boolean hasNext() 

Get the next record

• return

reset

public void reset() 

List of label strings

• return

nextRecord

public Record nextRecord() 

Load the record from the given DataInputStreamUnlike {- link #next()} the internal state of the RecordReader is not modifiedImplementations of this method should not close the DataInputStream

• param uri
• param dataInputStream
• throws IOException if error occurs during reading from the input stream

loadFromMetaData

public Record loadFromMetaData(RecordMetaData recordMetaData) throws IOException 

Load a single record from the given {- link RecordMetaData} instanceNote: that for data that isn’t splittable (i.e., text data that needs to be scanned/split), it is more efficient toload multiple records at once using {- link #loadFromMetaData(List)}

• param recordMetaData Metadata for the record that we want to load from
• return Single record for the given RecordMetaData instance
• throws IOException If I/O error occurs during loading

setListeners

public void setListeners(RecordListener... listeners) 

Load multiple records from the given a list of {- link RecordMetaData} instances

• param recordMetaDatas Metadata for the records that we want to load from
• return Multiple records for the given RecordMetaData instances
• throws IOException If I/O error occurs during loading

setListeners

public void setListeners(Collection<RecordListener> listeners) 

Set the record listeners for this record reader.

• param listeners

close

public void close() throws IOException 

Closes this stream and releases any system resources associatedwith it. If the stream is already closed then invoking thismethod has no effect.

As noted in {- link AutoCloseable#close()}, cases where theclose may fail require careful attention. It is strongly advisedto relinquish the underlying resources and to internallymark the {- code Closeable} as closed, prior to throwingthe {- code IOException}.

• throws IOException if an I/O error occurs

NativeAudioRecordReader

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Native audio file loader using FFmpeg.

WavFileRecordReader

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Wav file loader

ImageRecordReader

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Image record reader.Reads a local file system and parses images of a givenheight and width.All images are rescaled and converted to the given height, width, and number of channels.

Also appends the label if specified(one of k encoding based on the directory structure where each subdir of the root is an indexed label)

TfidfRecordReader

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TFIDF record reader (wraps a tfidf vectorizerfor delivering labels and conforming to the record reader interface)