forEachRight
Invoke a function for each element in a collection, iterating from the right to left.
Usage
var forEachRight = require( '@stdlib/utils/for-each-right' );
forEachRight( collection, fcn[, thisArg ] )
Invokes a function
for each element in a collection
, iterating from right to left.
function log( value, index ) {
console.log( '%s: %d', index, value );
}
var arr = [ 1, 2, 3, 4 ];
forEachRight( arr, log );
/* =>
3: 4
2: 3
1: 2
0: 1
*/
The invoked function
is provided three arguments:
- value: collection element.
- index: collection index.
- collection: input collection.
Basic support for dynamic collections is provided. Note, however, that index incrementation is not guaranteed to be monotonically decreasing.
var arr = [ 1, 2, 3, 4 ];
var i = 0;
function log1( value, index, collection ) {
console.log( '%s: %d', index, value );
i += 1;
if ( index === 0 && collection.length < 10 ) {
collection.unshift( i+1 );
}
}
forEachRight( arr, log1 );
/* =>
3: 4
2: 3
1: 2
0: 1
0: 5
0: 6
0: 7
0: 8
0: 9
0: 10
*/
function log2( value, index, collection ) {
console.log( '%s: %d', index, value );
collection.pop();
}
arr = [ 1, 2, 3, 4 ];
forEachRight( arr, log2 );
/* =>
3: 4
1: 2
*/
To set the function execution context, provide a thisArg
.
function sum( value ) {
this.sum += value;
this.count += 1;
}
var arr = [ 1, 2, 3, 4 ];
var context = {
'sum': 0,
'count': 0
};
forEachRight( arr, sum, context );
var mean = context.sum / context.count;
// returns 2.5
Notes
A
collection
may be either anArray
,Typed Array
, or an array-likeObject
(excludingstrings
andfunctions
).The function differs from
Array.prototype.forEach
in the following ways:The function returns the input
collection
.The function does not skip
undefined
elements.function log( value, index ) { console.log( '%s: %s', index, value ); } var arr = [ 1, , , 4 ]; forEachRight( arr, log ); /* => 3: 4 2: undefined 1: undefined 0: 1 */
The function provides limited support for dynamic collections (i.e., collections whose
length
changes during execution).
Examples
var isEven = require( '@stdlib/assert/is-even' ).isPrimitive;
var forEachRight = require( '@stdlib/utils/for-each-right' );
var arr;
var i;
function log( value, index, collection ) {
console.log( '%s: %d', index, value );
i += 1;
if ( isEven( i ) ) {
collection.pop();
} else {
collection.unshift( i+1 );
}
}
arr = new Array( 100 );
for ( i = arr.length-1; i >= 0; i-- ) {
arr[ i ] = i;
}
i = 0;
forEachRight( arr, log );