arrayview2iterator
Create an iterator from an array-like object view.
Usage
var arrayview2iterator = require( '@stdlib/array/to-view-iterator' );
arrayview2iterator( src[, begin[, end]][, mapFcn[, thisArg]] )
Returns an iterator which iterates over each element in an array-like object view.
var it = arrayview2iterator( [ 1, 2, 3, 4 ] );
// returns <Object>
var v = it.next().value;
// returns 1
v = it.next().value;
// returns 2
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
valueproperty and adoneproperty having abooleanvalue indicating whether the iterator is finished. - return: function which closes an iterator and returns a single (optional) argument in an iterator protocol-compliant object.
By default, the returned iterator begins iterating from the first element in an array-like object. To specify an alternative starting index, provide a begin argument (inclusive).
var it = arrayview2iterator( [ 1, 2, 3, 4 ], 1 );
// returns <Object>
var 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
If begin is less than 0, the starting index is resolved relative to the last element. For example, the following generates the same behavior as in the previous example
var it = arrayview2iterator( [ 1, 2, 3, 4 ], -3 );
// returns <Object>
var 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
By default, the returned iterator iterates until the last element in an array-like object. To specify an alternative ending index, provide an end argument (non-inclusive).
var it = arrayview2iterator( [ 1, 2, 3, 4 ], 0, 3 );
// returns <Object>
var v = it.next().value;
// returns 1
v = it.next().value;
// returns 2
v = it.next().value;
// returns 3
var bool = it.next().done;
// returns true
If end is less than 0, the ending index is resolved relative to the last element. For example, the following generates the same behavior as in the previous example
var it = arrayview2iterator( [ 1, 2, 3, 4 ], 0, -1 );
// returns <Object>
var v = it.next().value;
// returns 1
v = it.next().value;
// returns 2
v = it.next().value;
// returns 3
var bool = it.next().done;
// returns true
To invoke a function for each src value, provide a callback function.
function fcn( v ) {
return v * 10.0;
}
var it = arrayview2iterator( [ 1, 2, 3, 4 ], 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 = arrayview2iterator( [ 1, 2, 3, 4 ], 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 = arrayview2iterator( [ 1, 2, 3, 4 ], 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-likeobjectbefore creating an iterator. Otherwise, any changes to the contents of an array-likeobjectwill be reflected in the returned iterator. - In environments supporting
Symbol.iterator, the function explicitly does not invoke an array's@@iteratormethod, 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 arrayview2iterator = require( '@stdlib/array/to-view-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 from an array view which scales iterated values:
var it = arrayview2iterator( arr, 40, 60, scale );
// Perform manual iteration...
var v;
while ( true ) {
v = it.next();
if ( v.done ) {
break;
}
console.log( v.value );
}