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README.md

iterDedupeBy

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

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 );
}

See Also