Strided Iterator

Create an iterator from a strided array-like object.

Usage

var stridedarray2iterator = require( '@stdlib/array/to-strided-iterator' );

stridedarray2iterator( N, src, stride, offset[, mapFcn[, thisArg]] )

Returns an iterator which iterates over elements in an array-like object according to specified stride parameters.

var values = [ 1, 2, 3, 4, 5, 6, 7, 8 ];

var N = 4;
var stride = -2;
var offset = 6;

var it = stridedarray2iterator( N, values, stride, offset );
// returns <Object>

var v = it.next().value;
// returns 7

v = it.next().value;
// returns 5

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

// ...

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.

To invoke a function for each src value, provide a callback function.

function fcn( v ) {
    return v * 10.0;
}

var it = stridedarray2iterator( 4, [ 1, 2, 3, 4 ], 1, 0, fcn );
// returns <Object>

var v = it.next().value;
// returns 10.0

v = it.next().value;
// returns 20.0

v = it.next().value;
// returns 30.0

// ...

The invoked function is provided four arguments:

  • value: iterated value.
  • index: iterated value index.
  • n: iteration count (zero-based).
  • src: source array-like object.
function fcn( v, i ) {
    return v * (i+1);
}

var it = stridedarray2iterator( 4, [ 1, 2, 3, 4 ], 1, 0, fcn );
// returns <Object>

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

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

v = it.next().value;
// returns 9

// ...

To set the callback function execution context, provide a thisArg.

function fcn( v ) {
    this.count += 1;
    return v * 10.0;
}

var ctx = {
    'count': 0
};

var it = stridedarray2iterator( 4, [ 1, 2, 3, 4 ], 1, 0, fcn, ctx );
// returns <Object>

var v = it.next().value;
// returns 10.0

v = it.next().value;
// returns 20.0

v = it.next().value;
// returns 30.0

var count = ctx.count;
// returns 3

Notes

  • If an environment supports Symbol.iterator, the returned iterator is iterable.
  • If provided a generic array, the returned iterator does not ignore holes. To achieve greater performance for sparse arrays, use a custom iterator.
  • A returned iterator does not copy a provided array-like object. To ensure iterable reproducibility, copy a provided array-like object before creating an iterator. Otherwise, any changes to the contents of an array-like object will be reflected in the returned iterator.
  • In environments supporting Symbol.iterator, the function explicitly does not invoke an array's @@iterator method, regardless of whether this method is defined. To convert an array to an implementation defined iterator, invoke this method directly.
  • The returned iterator supports array-like objects having getter and setter accessors for array element access (e.g., @stdlib/array/complex64).

Examples

var Float64Array = require( '@stdlib/array/float64' );
var inmap = require( '@stdlib/utils/inmap' );
var randu = require( '@stdlib/random/base/randu' );
var stridedarray2iterator = require( '@stdlib/array/to-strided-iterator' );

function scale( v, i ) {
    return v * (i+1);
}

// Create an array filled with random numbers:
var arr = inmap( new Float64Array( 100 ), randu );

// Create an iterator which scales every fourth value in reverse order:
var it = stridedarray2iterator( 25, arr, -4, 99, scale );

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

See Also

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