Iterator Stream

Create a readable stream from an iterator.

Installation

npm install @stdlib/streams-node-from-iterator

Usage

var iteratorStream = require( '@stdlib/streams-node-from-iterator' );

iteratorStream( iterator[, options] )

Returns a readable stream from an iterator.

var inspectStream = require( '@stdlib/streams-node-inspect-sink' );
var randu = require( '@stdlib/random-iter-randu' );

var iStream;
var stream;

function log( chunk, idx ) {
    console.log( chunk.toString() );
    if ( idx === 10 ) {
        stream.destroy();
    }
}

stream = iteratorStream( randu() );
iStream = inspectStream( log );

stream.pipe( iStream );

The function accepts the following options:

• objectMode: specifies whether a stream should operate in objectMode. Default: false.
• encoding: specifies how Buffer objects should be decoded to strings. Default: null.
• highWaterMark: specifies the maximum number of bytes to store in an internal buffer before pausing iteration.
• sep: separator used to join streamed data. This option is only applicable when a stream is not in objectMode. Default: '\n'.
• serialize: custom serialization function. This option is only applicable when a stream is not in objectMode.

To set stream options,

var randu = require( '@stdlib/random-iter-randu' );

var opts = {
    'objectMode': true,
    'encoding': 'utf8',
    'highWaterMark': 64
};

var stream = iteratorStream( randu(), opts );

By default, when not operating in objectMode, a returned stream delineates iterated values using a newline character. To specify an alternative separator, set the sep option.

var inspectStream = require( '@stdlib/streams-node-inspect-sink' );
var randu = require( '@stdlib/random-iter-randu' );

function log( chunk ) {
    console.log( chunk.toString() );
}

var it = randu({
    'iter': 10
});

var stream = iteratorStream( it, {
    'sep': ','
});

var iStream = inspectStream( log );

stream.pipe( iStream );

By default, when not operating in objectMode, a returned stream serializes iterated values as JSON strings. To specify custom serialization behavior (either to a string or Buffer), set the serialize option.

var inspectStream = require( '@stdlib/streams-node-inspect-sink' );
var randu = require( '@stdlib/random-iter-randu' );

function serialize( v ) {
    return 'r::' + v.toString();
}

function log( chunk ) {
    console.log( chunk.toString() );
}

var it = randu({
    'iter': 10
});

var stream = iteratorStream( it, {
    'serialize': serialize
});

var iStream = inspectStream( log );

stream.pipe( iStream );

iteratorStream.factory( [options] )

Returns a function for creating readable streams from iterators.

var randu = require( '@stdlib/random-iter-randu' );

var opts = {
    'objectMode': true,
    'encoding': 'utf8',
    'highWaterMark': 64
};

var createStream = iteratorStream.factory( opts );

var stream1 = createStream( randu() );
var stream2 = createStream( randu() );
// ...

The method accepts the same options as iteratorStream().

iteratorStream.objectMode( iterator[, options] )

This method is a convenience function to create streams which always operate in objectMode.

var inspectStream = require( '@stdlib/streams-node-inspect-sink' );
var randu = require( '@stdlib/random-iter-randu' );

function log( v ) {
    console.log( v );
}

var opts = {
    'iter': 10
};
var stream = iteratorStream.objectMode( randu( opts ) );

opts = {
    'objectMode': true
};
var iStream = inspectStream( opts, log );

stream.pipe( iStream );

This method accepts the same options as iteratorStream(); however, the method will always override the objectMode option in options.

Notes

• In objectMode, null is a reserved value. If an iterator generates null values (e.g., as a means to encode missing values), the stream will prematurely end. Consider an alternative encoding or explicitly map null values to a different value by wrapping the provided iterator with another iterator.
• In binary mode, if an iterator generates undefined values, the stream will emit an error. Consider providing a custom serialization function or explicitly map undefined values to a different value by wrapping the provided iterator with another iterator.

Examples

var inspectStream = require( '@stdlib/streams-node-inspect-sink' );
var randu = require( '@stdlib/random-iter-randu' );
var iteratorStream = require( '@stdlib/streams-node-from-iterator' );

function log( v ) {
    console.log( v.toString() );
}

// Create an iterator which generates uniformly distributed pseudorandom numbers:
var opts = {
    'iter': 10
};
var it = randu( opts );

// Convert the iterator to a stream:
opts = {
    'objectMode': true
};
var stream = iteratorStream( it, opts );

// Create a writable stream for inspecting stream data:
opts = {
    'objectMode': true
};
var iStream = inspectStream( opts, log );

// Begin data flow:
stream.pipe( iStream );

See Also

• @stdlib/streams-node/from-array: create a readable stream from an array-like object.

Notice

This package is part of stdlib, a standard library for JavaScript and Node.js, with an emphasis on numerical and scientific computing. The library provides a collection of robust, high performance libraries for mathematics, statistics, streams, utilities, and more.

For more information on the project, filing bug reports and feature requests, and guidance on how to develop stdlib, see the main project repository.

Community

License

See LICENSE.

Copyright

Copyright © 2016-2024. The Stdlib Authors.