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mapReduceRight
Perform a single-pass map-reduce operation against each element in an array while iterating from right to left and return the accumulated result.
Installation
npm install @stdlib/utils-map-reduce-right
Usage
var mapReduceRight = require( '@stdlib/utils-map-reduce-right' );
mapReduceRight( arr, initial, mapper, reducer[, thisArg ] )
Performs a map-reduce operation against each element in an array while iterating from right to left and returns the accumulated result.
function square( value ) {
return value * value;
}
function sum( accumulator, value ) {
return accumulator + value;
}
var arr = [ 1, 2, 3, 4 ];
var out = mapReduceRight( arr, 0, square, sum );
The function accepts both array-like objects and ndarray
-like objects.
var array = require( '@stdlib/ndarray-array' );
function square( value ) {
return value * value;
}
function sum( accumulator, value ) {
return accumulator + value;
}
var opts = {
'dtype': 'generic'
};
var arr = array( [ [ 1, 2, 3 ], [ 4, 5, 6 ] ], opts );
var out = mapReduceRight( arr, 0, square, sum );
The mapping function is provided the following arguments:
- value: array element.
- index: element index.
- arr: input array.
The reducing function is provided the following arguments:
- accumulator: accumulated value.
- value: result of applying the mapping function to the current array element.
- index: element index.
- arr: input array.
To set the this
context when invoking the reducing function, provide a thisArg
.
function square( value ) {
return value * value;
}
function sum( accumulator, value ) {
this.count += 1;
return accumulator + value;
}
var arr = [ 1, 2, 3, 4 ];
var ctx = {
'count': 0
};
var out = mapReduceRight( arr, 0, square, sum, ctx );
var mean = out / ctx.count;
Notes
-
The function supports array-like objects exposing getters and setters for array element access (e.g., Complex64Array
, Complex128Array
, etc).
var Complex64Array = require( '@stdlib/array-complex64' );
var Complex64 = require( '@stdlib/complex-float32' );
var cceil = require( '@stdlib/math-base-special-cceil' );
var realf = require( '@stdlib/complex-realf' );
var imagf = require( '@stdlib/complex-imagf' );
function sum( acc, z ) {
var re1 = realf( acc );
var im1 = imagf( acc );
var re2 = realf( z );
var im2 = imagf( z );
return new Complex64( re1+re2, im1+im2 );
}
var x = new Complex64Array( [ 1.5, 2.5, 3.5, 4.5, 5.5, 6.5, 7.5, 8.5 ] );
var v = mapReduceRight( x, new Complex64( 0.0, 0.0 ), cceil, sum );
var re = realf( v );
var im = imagf( v );
-
For ndarray
-like objects, the function performs a single-pass map-reduce operation over the entire input ndarray
(i.e., higher-order ndarray
dimensions are flattened to a single-dimension).
-
When applying a function to ndarray
-like objects, performance will be best for ndarray
-like objects which are single-segment contiguous.
Examples
var filledarrayBy = require( '@stdlib/array-filled-by' );
var discreteUniform = require( '@stdlib/random-base-discrete-uniform' ).factory;
var naryFunction = require( '@stdlib/utils-nary-function' );
var add = require( '@stdlib/math-base-ops-add' );
var abs = require( '@stdlib/math-base-special-abs' );
var array = require( '@stdlib/ndarray-array' );
var mapReduceRight = require( '@stdlib/utils-map-reduce-right' );
function fill( i ) {
var rand = discreteUniform( -10*(i+1), 10*(i+1) );
return filledarrayBy( 10, 'generic', rand );
}
var x = array( filledarrayBy( 10, 'generic', fill ), {
'dtype': 'generic',
'flatten': true
});
var f1 = naryFunction( abs, 1 );
var f2 = naryFunction( add, 2 );
var out = mapReduceRight( x, 0, f1, f2 );
console.log( 'x:' );
console.log( x.data );
console.log( 'sum: %d', out );
See Also
@stdlib/utils-map-right
: apply a function to each element in an array and assign the result to an element in an output array, iterating from right to left.@stdlib/utils-map-reduce
: perform a single-pass map-reduce operation against each element in an array and return the accumulated result.@stdlib/utils-reduce-right
: apply a function against an accumulator and each element in an array while iterating from right to left and return the accumulated result.
Notice
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.
License
See LICENSE.
Copyright
Copyright © 2016-2024. The Stdlib Authors.