@stdlib/iter-dedupe-by

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iterDedupeBy

Create an iterator which removes consecutive values that resolve to the same value according to a provided function.

Installation

npm install @stdlib/iter-dedupe-by

Usage

var iterDedupeBy = require( '@stdlib/iter-dedupe-by' );

iterDedupeBy( iterator, [limit,] fcn )

Returns an iterator which removes consecutive values that resolve to the same value according to a provided function.

var array2iterator = require( '@stdlib/array-to-iterator' );

function fcn( v ) {
    return v;
}

var arr = array2iterator( [ 1, 1, 2, 3, 3, 3, 4, 4 ] );
var it = iterDedupeBy( arr, fcn );
// returns <Object>

var v = it.next().value;
// returns 1

v = it.next().value;
// returns 2

v = it.next().value;
// returns 3

v = it.next().value;
// returns 4

var bool = it.next().done;
// returns true

The returned iterator protocol-compliant object has the following properties:

• next: function which returns an iterator protocol-compliant object containing the next iterated value (if one exists) assigned to a value property and a done property having a boolean value indicating whether the iterator is finished.
• return: function which closes an iterator and returns a single (optional) argument in an iterator protocol-compliant object.

The callback function is provided five arguments:

• curr: current source iterated value.
• sprev: previous source iterated value.
• dprev: previous downstream iterated value.
• index: source iteration index (zero-based).
• acc: previous resolved value.

The returned iterator removes consecutive values which resolve to the same value and does not return globally "unique" values.

var array2iterator = require( '@stdlib/array-to-iterator' );

function fcn( v ) {
    return v;
}

var arr = array2iterator( [ 1, 1, 2, 1, 1, 2 ] );
var it = iterDedupeBy( arr, fcn );
// returns <Object>

var v = it.next().value;
// returns 1

v = it.next().value;
// returns 2

v = it.next().value;
// returns 1

v = it.next().value;
// returns 2

var bool = it.next().done;
// returns true

To specify the number of allowed consecutive duplicated values, provide a limit argument.

var array2iterator = require( '@stdlib/array-to-iterator' );

function fcn( v ) {
    return v;
}

var arr = array2iterator( [ 1, 1, 2, 3, 3, 3, 3, 4, 4, 4 ] );
var it = iterDedupeBy( arr, 2, fcn );
// returns <Object>

var v = it.next().value;
// returns 1

v = it.next().value;
// returns 1

v = it.next().value;
// returns 2

v = it.next().value;
// returns 3

v = it.next().value;
// returns 3

v = it.next().value;
// returns 4

v = it.next().value;
// returns 4

var bool = it.next().done;
// returns true

Notes

• If an environment supports Symbol.iterator and a provided iterator is iterable, the returned iterator is iterable.

Examples

var randi = require( '@stdlib/random-iter-discrete-uniform' );
var iterDedupe = require( '@stdlib/iter-dedupe' );
var iterDedupeBy = require( '@stdlib/iter-dedupe-by' );

function fcn( curr, sprev, dprev, i, acc ) {
    if ( curr < dprev ) {
        return 1;
    }
    if ( curr === dprev ) {
        return acc; // ensures that duplicate values are removed
    }
    // curr > dprev
    return -1;
}

// Create a seeded iterator for generating pseudorandom integers:
var rand = randi( 1, 10, {
    'seed': 1234,
    'iter': 100
});

// Create an iterator which removes consecutive duplicated values:
var deduped = iterDedupe( rand );

// Create an iterator which forces consecutive values to follow an alternating less than, greater than pattern:
var it = iterDedupeBy( deduped, fcn );

// Perform manual iteration...
var v;
while ( true ) {
    v = it.next();
    if ( v.done ) {
        break;
    }
    console.log( v.value );
}

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See Also

• @stdlib/iter-dedupe: create an iterator which removes consecutive duplicated values.
• @stdlib/iter-unique: create an iterator which returns unique values.

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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

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License

See LICENSE.

Copyright

Copyright © 2016-2024. The Stdlib Authors.