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Create an iterator which, while a test condition is false, invokes a function for each iterated value before returning the iterated value.
npm install @stdlib/iter-until-each
var iterUntilEach = require( '@stdlib/iter-until-each' );
Returns an iterator which invokes a function for each iterated value before returning the iterated value until either a predicate
function returns true
or the iterator has iterated over all values.
var array2iterator = require( '@stdlib/array-to-iterator' );
function predicate( v ) {
return v > 2;
}
function assert( v ) {
if ( v !== v ) {
throw new Error( 'should not be NaN' );
}
}
var it = iterUntilEach( array2iterator( [ 1, 2, 3, 4 ] ), predicate, assert );
// returns {}
var r = it.next().value;
// returns 1
r = it.next().value;
// returns 2
r = it.next().value;
// undefined
// ...
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 adone
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.
Both the predicate
function and the function to invoke for each iterated value are provided two arguments:
- value: iterated value
- index: iteration index (zero-based)
var array2iterator = require( '@stdlib/array-to-iterator' );
function predicate( v ) {
return v > 2;
}
function assert( v, i ) {
if ( i > 1 ) {
throw new Error( 'unexpected error' );
}
}
var it = iterUntilEach( array2iterator( [ 1, 2, 3, 4 ] ), predicate, assert );
// returns <Object>
var r = it.next().value;
// returns 1
r = it.next().value;
// returns 2
r = it.next().value;
// undefined
// ...
To set the execution context for fcn
, provide a thisArg
.
var array2iterator = require( '@stdlib/array-to-iterator' );
function assert( v ) {
this.count += 1;
if ( v !== v ) {
throw new Error( 'should not be NaN' );
}
}
function predicate( v ) {
return v > 2;
}
var ctx = {
'count': 0
};
var it = iterUntilEach( array2iterator( [ 1, 2, 3 ] ), predicate, assert, ctx );
// returns <Object>
var r = it.next().value;
// returns 1
r = it.next().value;
// returns 2
var count = ctx.count;
// returns 2
- If an environment supports
Symbol.iterator
and a provided iterator is iterable, the returned iterator is iterable.
var randu = require( '@stdlib/random-iter-randu' );
var isnan = require( '@stdlib/math-base-assert-is-nan' );
var iterUntilEach = require( '@stdlib/iter-until-each' );
function assert( v ) {
if ( isnan( v ) ) {
throw new Error( 'should not be NaN' );
}
}
function predicate( v ) {
return v <= 0.75;
}
// Create a seeded iterator for generating pseudorandom numbers:
var rand = randu({
'seed': 1234,
'iter': 10
});
// Create an iterator which validates generated numbers:
var it = iterUntilEach( rand, predicate, assert );
// Perform manual iteration...
var r;
while ( true ) {
r = it.next();
if ( r.done ) {
break;
}
console.log( r.value );
}
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.
See LICENSE.
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