mapAccumRight.js•1.36 kB
var _curry3 = require('./internal/_curry3');
/**
* The mapAccumRight function behaves like a combination of map and reduce; it
* applies a function to each element of a list, passing an accumulating
* parameter from right to left, and returning a final value of this
* accumulator together with the new list.
*
* Similar to `mapAccum`, except moves through the input list from the right to
* the left.
*
* The iterator function receives two arguments, *acc* and *value*, and should
* return a tuple *[acc, value]*.
*
* @func
* @memberOf R
* @since v0.10.0
* @category List
* @sig (acc -> x -> (acc, y)) -> acc -> [x] -> (acc, [y])
* @param {Function} fn The function to be called on every element of the input `list`.
* @param {*} acc The accumulator value.
* @param {Array} list The list to iterate over.
* @return {*} The final, accumulated value.
* @see R.addIndex
* @example
*
* var digits = ['1', '2', '3', '4'];
* var append = (a, b) => [a + b, a + b];
*
* R.mapAccumRight(append, 0, digits); //=> ['04321', ['04321', '0432', '043', '04']]
*/
module.exports = _curry3(function mapAccumRight(fn, acc, list) {
var idx = list.length - 1;
var result = [];
var tuple = [acc];
while (idx >= 0) {
tuple = fn(tuple[0], list[idx]);
result[idx] = tuple[1];
idx -= 1;
}
return [tuple[0], result];
});