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Split values into two groups according to a predicate function.
npm install @stdlib/utils-async-bifurcate-by
Alternatively,
- To load the package in a website via a
script
tag without installation and bundlers, use the ES Module available on theesm
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umd
branch (see README).
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var bifurcateByAsync = require( '@stdlib/utils-async-bifurcate-by' );
Splits values into two groups according to a predicate
function, which specifies which group an element in the input collection
belongs to. If a predicate
function calls a provided callback with a truthy group value, a collection element belongs to the first group; otherwise, a collection element belongs to the second group.
function predicate( value, next ) {
setTimeout( onTimeout, value );
function onTimeout() {
console.log( value );
next( null, (value > 2000) );
}
}
function done( error, result ) {
if ( error ) {
throw error;
}
console.log( result );
}
var arr = [ 3000, 2500, 1000 ];
bifurcateByAsync( arr, predicate, done );
/* =>
1000
2500
3000
[ [ 2500, 3000 ], [ 1000 ] ]
*/
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 thepredicate
function for eachcollection
element. Iftrue
, the function setsoptions.limit=1
. Default:false
.returns
: specifies the output format. If the option equals'values'
, the function returns group results as element values. If the option equals'indices'
, the function returns group results as element indices. If the option equals'*'
, the function returns group results as both element indices and values. Default:'values'
.thisArg
: the execution context forpredicate
.
By default, the function returns group results as element values. To return element indices, set the returns
option to 'indices'
.
function predicate( value, next ) {
setTimeout( onTimeout, value );
function onTimeout() {
console.log( value );
next( null, (value > 2000) );
}
}
function done( error, result ) {
if ( error ) {
throw error;
}
console.log( result );
}
var arr = [ 3000, 2500, 1000 ];
var opts = {
'returns': 'indices'
};
bifurcateByAsync( arr, opts, predicate, done );
/* =>
1000
2500
3000
[ [ 1, 0 ], [ 2 ] ]
*/
To return index-value pairs, set the returns
option to '*'
.
function predicate( value, next ) {
setTimeout( onTimeout, value );
function onTimeout() {
console.log( value );
next( null, (value > 2000) );
}
}
function done( error, result ) {
if ( error ) {
throw error;
}
console.log( result );
}
var arr = [ 3000, 2500, 1000 ];
var opts = {
'returns': '*'
};
bifurcateByAsync( arr, opts, predicate, done );
/* =>
1000
2500
3000
[ [ [ 1, 2500 ], [ 0, 3000 ] ], [ [ 2, 1000 ] ] ]
*/
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, (value > 2000) );
}
}
function done( error, result ) {
if ( error ) {
throw error;
}
console.log( result );
}
var arr = [ 3000, 2500, 1000 ];
var opts = {
'series': true
};
bifurcateByAsync( arr, opts, predicate, done );
/* =>
3000
2500
1000
[ [ 3000, 2500 ], [ 1000 ] ]
*/
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, (value > 2000) );
}
}
function done( error, result ) {
if ( error ) {
throw error;
}
console.log( result );
}
var arr = [ 3000, 2500, 1000 ];
var opts = {
'limit': 2
};
bifurcateByAsync( arr, opts, predicate, done );
/* =>
2500
3000
1000
[ [ 2500, 3000 ], [ 1000 ] ]
*/
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() {
next( null, (value > 2000) );
}
}
var arr = [ 3000, 2500, 1000 ];
var context = {
'count': 0
};
var opts = {
'thisArg': context
};
bifurcateByAsync( arr, opts, predicate, done );
function done( error, result ) {
if ( error ) {
throw error;
}
console.log( result );
// => [ [ 2500, 3000 ], [ 1000 ] ]
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 inputcollection
.next
: a callback which should be called once thepredicate
function has finished processing a collectionvalue
.
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, (value > 2000) );
}
}
function done( error, result ) {
if ( error ) {
throw error;
}
console.log( result );
}
var arr = [ 3000, 2500, 1000 ];
bifurcateByAsync( arr, predicate, done );
/* =>
collection: 3000,2500,1000. 0: 3000
collection: 3000,2500,1000. 1: 2500
collection: 3000,2500,1000. 2: 1000
1000
2500
3000
[ [ 2500, 3000 ], [ 1000 ] ]
*/
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, (value > 2000) );
}
}
function done( error, result ) {
if ( error ) {
throw error;
}
console.log( result );
}
var f = bifurcateByAsync.factory( predicate );
var arr1 = [ 3000, 2500, 1000 ];
f( arr1, done );
/* =>
1000
2500
3000
[ [ 2500, 3000 ], [ 1000 ] ]
*/
var arr2 = [ 300, 250, 100 ];
f( arr2, done );
/* =>
100
250
300
[ [], [ 100, 250, 300 ] ]
*/
The function accepts the same options
as bifurcateByAsync()
.
- A
collection
may be either anArray
,Typed Array
, or an array-likeObject
(excludingstrings
andfunctions
). - If a provided function calls the
next
callback with a truthyerror
argument, the function suspends execution and immediately calls thedone
callback for subsequenterror
handling. - The function does not support dynamic
collection
resizing. - The function does not skip
undefined
elements. - If provided an empty
collection
, the function calls thedone
callback with an emptyarray
for the group results. - Neither
bifurcateByAsync
nor the function returned by thefactory
method guarantee asynchronous execution. To guarantee asynchrony, wrap thedone
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
).
var resolve = require( 'path' ).resolve;
var readFile = require( '@stdlib/fs-read-file' );
var bifurcateByAsync = require( '@stdlib/utils-async-bifurcate-by' );
var files = [
resolve( __dirname, 'package.json' ),
resolve( __dirname, 'README.md' ),
resolve( __dirname, 'beep.boop.md' )
];
function done( error, result ) {
if ( error ) {
throw error;
}
console.log( result );
}
function predicate( file, next ) {
var opts = {
'encoding': 'utf8'
};
readFile( file, opts, onFile );
function onFile( error ) {
if ( error ) {
return next( null, false );
}
next( null, true );
}
}
bifurcateByAsync( files, predicate, done );
@stdlib/utils-bifurcate-by
: split values into two groups according to a predicate function.@stdlib/utils-async/group-by
: group values according to an indicator function.
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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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