someByAsync

Test whether a collection contains at least n elements which pass a test implemented by a predicate function.

Usage

var someByAsync = require( '@stdlib/utils/some-by-async' );

someByAsync( collection, n, [options,] predicate, done )

Tests whether a collection contains at least n elements which pass a test implemented by a predicate function.

function predicate( value, next ) {
    setTimeout( onTimeout, value );
    function onTimeout() {
        console.log( value );
        next( null, false );
    }
}

function done( error, bool ) {
    if ( error ) {
        throw error;
    }
    console.log( bool );
}

var arr = [ 3000, 2500, 1000 ];

someByAsync( arr, 2, predicate, done );
/* =>
    1000
    2500
    3000
    false
*/

The function immediately stops processing collection elements and returns true for the test result upon receiving n truthy predicate result values.

function predicate( value, index, next ) {
    setTimeout( onTimeout, value );
    function onTimeout() {
        if ( index === 1 ) {
            return next( new Error( 'beep' ) );
        }
        next( null, true );
    }
}

function done( error, bool ) {
    if ( error ) {
        throw error;
    }
    console.log( bool );
}

var arr = [ 3000, 2500, 1000 ];

someByAsync( arr, 1, predicate, done );
// => true

The function accepts the following options:

  • limit: the maximum number of pending invocations at any one time. Default: infinity.
  • series: boolean indicating whether to sequentially invoke the predicate function for each collection element. If true, the function sets options.limit=1. Default: false.
  • thisArg: the execution context for fcn.

By default, all elements are processed concurrently, which means that the function does not guarantee completion order. To process each collection element sequentially, set the series option to true.

function predicate( value, next ) {
    setTimeout( onTimeout, value );
    function onTimeout() {
        console.log( value );
        next( null, false );
    }
}

function done( error, bool ) {
    if ( error ) {
        throw error;
    }
    console.log( bool );
}

var arr = [ 3000, 2500, 1000 ];

var opts = {
    'series': true
};

someByAsync( arr, 2, opts, predicate, done );
/* =>
    3000
    2500
    1000
    false
*/

To limit the maximum number of pending function invocations, set the limit option.

function predicate( value, next ) {
    setTimeout( onTimeout, value );
    function onTimeout() {
        console.log( value );
        next( null, false );
    }
}

function done( error, bool ) {
    if ( error ) {
        throw error;
    }
    console.log( bool );
}

var arr = [ 3000, 2500, 1000 ];

var opts = {
    'limit': 2
};

someByAsync( arr, 2, opts, predicate, done );
/* =>
    2500
    3000
    1000
    false
*/

To set the execution context of the predicate function, set the thisArg option.

function predicate( value, next ) {
    this.count += 1;
    setTimeout( onTimeout, value );
    function onTimeout() {
        console.log( value );
        next( null, false );
    }
}

function done( error, bool ) {
    if ( error ) {
        throw error;
    }
    console.log( bool );
}

var arr = [ 3000, 2500, 1000 ];

var context = {
    'count': 0
};

var opts = {
    'thisArg': context
};

someByAsync( arr, 2, opts, predicate, done );
/* =>
    1000
    2500
    3000
    false
*/

console.log( context.count );
// => 3

When invoked, the predicate function is provided a maximum of four arguments:

  • value: collection value.
  • index: collection index.
  • collection: the input collection.
  • next: a callback which should be called once the predicate function has finished processing a collection value.

The actual number of provided arguments depends on function length. If the predicate function accepts two arguments, the predicate function is provided value and next. If the predicate function accepts three arguments, the predicate function is provided value, index, and next. For every other predicate function signature, the predicate function is provided all four arguments.

function predicate( value, i, collection, next ) {
    console.log( 'collection: %s. %d: %d', collection.join( ',' ), i, value );
    setTimeout( onTimeout, value );
    function onTimeout() {
        console.log( value );
        next( null, false );
    }
}

function done( error, bool ) {
    if ( error ) {
        throw error;
    }
    console.log( bool );
}

var arr = [ 3000, 2500, 1000 ];

someByAsync( arr, 2, predicate, done );
/* =>
    collection: 3000,2500,1000. 0: 3000
    collection: 3000,2500,1000. 1: 2500
    collection: 3000,2500,1000. 2: 1000
    1000
    2500
    3000
    false
*/

someByAsync.factory( [options,] predicate )

Returns a function which invokes a predicate function once for each element in a collection.

function predicate( value, next ) {
    setTimeout( onTimeout, value );
    function onTimeout() {
        console.log( value );
        next( null, false );
    }
}

function done( error, bool ) {
    if ( error ) {
        throw error;
    }
    console.log( bool );
}

var f = someByAsync.factory( predicate );

var arr1 = [ 3000, 2500, 1000 ];

f( arr1, 2, done );
/* =>
    1000
    2500
    3000
    false
*/

var arr2 = [ 300, 250, 100 ];

f( arr2, 2, done );
/* =>
    100
    250
    300
    false
*/

The function accepts the same options as someByAsync().

Notes

  • A collection may be either an Array, Typed Array, or an array-like Object (excluding strings and functions).
  • If a provided function calls the next callback with a truthy error argument, the function suspends execution and immediately calls the done callback for subsequent error handling.
  • The function does not support dynamic collection resizing.
  • The function does not skip undefined elements.
  • If provided an empty collection, the function calls the done callback with false as the test result.
  • Neither someByAsync nor the function returned by the factory method guarantee asynchronous execution. To guarantee asynchrony, wrap the done callback in a function which either executes at the end of the current stack (e.g., nextTick) or during a subsequent turn of the event loop (e.g., setImmediate, setTimeout).

Examples

var resolve = require( 'path' ).resolve;
var readFile = require( '@stdlib/fs/read-file' );
var someByAsync = require( '@stdlib/utils/some-by-async' );

var files = [
    resolve( __dirname, 'package.json' ),
    resolve( __dirname, 'README.md' )
];

function done( error, bool ) {
    if ( error ) {
        throw error;
    }
    if ( bool ) {
        console.log( 'Successfully read some files.' );
    } else {
        console.log( 'Unable to read some files.' );
    }
}

function predicate( file, next ) {
    var opts = {
        'encoding': 'utf8'
    };
    readFile( file, opts, onFile );

    function onFile( error ) {
        if ( error ) {
            return next( null, false );
        }
        next( null, true );
    }
}

someByAsync( files, 2, predicate, done );