iterStridedBy

Create an iterator which steps according to a provided callback function.

Usage

var iterStridedBy = require( '@stdlib/iter/strided-by' );

iterStridedBy( iterator, fcn[, offset[, eager]][, thisArg] )

Returns an iterator which steps according to a provided callback function.

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

function stride( v, i ) {
    return (i % 10) + 1;
}

var arr = array2iterator( [ 1, 2, 3, 4, 5, 6, 7, 8 ] );
var it = iterStridedBy( arr, stride );
// returns <Object>

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

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

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

// ...

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 four arguments:

  • value: iterated value
  • i: source iteration index (zero-based)
  • n: iteration index (zero-based)
  • curr: current stride

To set the callback execution context, provide a thisArg.

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

function stride( v, i ) {
    this.count += 1;
    return (i % 10) + 1;
}

var ctx = {
    'count': 0
};

var arr = array2iterator( [ 1, 2, 3, 4, 5, 6, 7, 8 ] );
var it = iterStridedBy( arr, stride, ctx );
// returns <Object>

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

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

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

v = it.next().value;
// returns 8

var count = ctx.count;
// returns 4

To skip the first N values of a provided iterator, provide an offset argument.

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

function stride( v, i ) {
    return (i % 10) + 1;
}

var arr = array2iterator( [ 1, 2, 3, 4, 5, 6, 7, 8 ] );
var it = iterStridedBy( arr, stride, 1 );
// returns <Object>

var r = it.next().value;
// returns 2

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

r = it.next().value;
// returns 8

// ...

By default, the returned iterator defers consuming the first N input iterator values until the first value of the returned iterator is consumed. To eagerly advance the input iterator, set the eager argument to true.

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

function stride() {
    return 1;
}

var arr = array2iterator( [ 1, 2, 3, 4, 5, 6, 7, 8 ] );
var it = iterStridedBy( arr, stride, 4, true );
// returns <Object>

var r = it.next().value;
// returns 5

r = it.next().value;
// returns 6

r = it.next().value;
// returns 7

// ...

Notes

  • A callback function must return a positive integer value.
  • If an environment supports Symbol.iterator and a provided iterator is iterable, the returned iterator is iterable.

Examples

var randu = require( '@stdlib/random/iter/randu' );
var discreteUniform = require( '@stdlib/random/base/discrete-uniform' ).factory;
var iterStridedBy = require( '@stdlib/iter/strided-by' );

// Create a seeded iterator for generating pseudorandom numbers:
var rand = randu({
    'seed': 1234,
    'iter': 10
});

// Create a PRNG for generating pseudorandom integers on the interval [1,10]:
var randi = discreteUniform( 1, 10, {
    'seed': 4321
});

// Create an iterator which randomly selects input iterator values:
var it = iterStridedBy( rand, randi );

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