- reduce_.reduce(list, memo, iterator, [context])
+ reduce_.reduce(list, iterator, memo, [context])
Aliases: inject, foldl
Also known as inject and foldl, reduce boils down a
@@ -270,12 +270,12 @@ _.map([1, 2, 3], function(num){ return num * 3 });
iterator.
-var sum = _.reduce([1, 2, 3], 0, function(memo, num){ return memo + num });
+var sum = _.reduce([1, 2, 3], function(memo, num){ return memo + num }, 0);
=> 6
- reduceRight_.reduceRight(list, memo, iterator, [context])
+ reduceRight_.reduceRight(list, iterator, memo, [context])
Alias: foldr
The right-associative version of reduce. Delegates to the
@@ -285,7 +285,7 @@ var sum = _.reduce([1, 2, 3], 0, function(memo, num){ return memo + num });
var list = [[0, 1], [2, 3], [4, 5]];
-var flat = _.reduceRight(list, [], function(a, b) { return a.concat(b); });
+var flat = _.reduceRight(list, function(a, b) { return a.concat(b); }, []);
=> [4, 5, 2, 3, 0, 1]
diff --git a/test/chaining.js b/test/chaining.js
index 55f0c8c0d..e633ba5ad 100644
--- a/test/chaining.js
+++ b/test/chaining.js
@@ -12,11 +12,11 @@ $(document).ready(function() {
var counts = _(lyrics).chain()
.map(function(line) { return line.split(''); })
.flatten()
- .reduce({}, function(hash, l) {
+ .reduce(function(hash, l) {
hash[l] = hash[l] || 0;
hash[l]++;
return hash;
- }).value();
+ }, {}).value();
ok(counts['a'] == 16 && counts['e'] == 10, 'counted all the letters in the song');
});
diff --git a/test/collections.js b/test/collections.js
index 3759a6495..eb449d690 100644
--- a/test/collections.js
+++ b/test/collections.js
@@ -53,22 +53,22 @@ $(document).ready(function() {
});
test('collections: reduce', function() {
- var sum = _.reduce([1, 2, 3], 0, function(sum, num){ return sum + num; });
+ var sum = _.reduce([1, 2, 3], function(sum, num){ return sum + num; }, 0);
equals(sum, 6, 'can sum up an array');
var context = {multiplier : 3};
- sum = _.reduce([1, 2, 3], 0, function(sum, num){ return sum + num * this.multiplier; }, context);
+ sum = _.reduce([1, 2, 3], function(sum, num){ return sum + num * this.multiplier; }, 0, context);
equals(sum, 18, 'can reduce with a context object');
- sum = _.inject([1, 2, 3], 0, function(sum, num){ return sum + num; });
+ sum = _.inject([1, 2, 3], function(sum, num){ return sum + num; }, 0);
equals(sum, 6, 'aliased as "inject"');
- sum = _([1, 2, 3]).reduce(0, function(sum, num){ return sum + num; });
+ sum = _([1, 2, 3]).reduce(function(sum, num){ return sum + num; }, 0);
equals(sum, 6, 'OO-style reduce');
});
test('collections: reduceRight', function() {
- var list = _.foldr([1, 2, 3], '', function(memo, num){ return memo + num; });
+ var list = _.foldr([1, 2, 3], function(memo, num){ return memo + num; }, '');
equals(list, '321', 'can perform right folds');
});
diff --git a/underscore.js b/underscore.js
index b0533cadc..a7274adea 100644
--- a/underscore.js
+++ b/underscore.js
@@ -92,8 +92,11 @@
// Reduce builds up a single result from a list of values, aka inject, or foldl.
// Delegates to JavaScript 1.8's native reduce if available.
- _.reduce = function(obj, memo, iterator, context) {
- if (nativeReduce && obj.reduce === nativeReduce) return obj.reduce(_.bind(iterator, context), memo);
+ _.reduce = function(obj, iterator, memo, context) {
+ if (nativeReduce && obj.reduce === nativeReduce) {
+ if (context) iterator = _.bind(iterator, context);
+ return obj.reduce(iterator, memo);
+ }
each(obj, function(value, index, list) {
memo = iterator.call(context, memo, value, index, list);
});
@@ -102,10 +105,13 @@
// The right-associative version of reduce, also known as foldr. Uses
// Delegates to JavaScript 1.8's native reduceRight if available.
- _.reduceRight = function(obj, memo, iterator, context) {
- if (nativeReduceRight && obj.reduceRight === nativeReduceRight) return obj.reduceRight(_.bind(iterator, context), memo);
+ _.reduceRight = function(obj, iterator, memo, context) {
+ if (nativeReduceRight && obj.reduceRight === nativeReduceRight) {
+ if (context) iterator = _.bind(iterator, context);
+ return obj.reduceRight(iterator, memo);
+ }
var reversed = _.clone(_.toArray(obj)).reverse();
- return _.reduce(reversed, memo, iterator, context);
+ return _.reduce(reversed, iterator, memo, context);
};
// Return the first value which passes a truth test.
@@ -277,11 +283,11 @@
// Return a completely flattened version of an array.
_.flatten = function(array) {
- return _.reduce(array, [], function(memo, value) {
+ return _.reduce(array, function(memo, value) {
if (_.isArray(value)) return memo.concat(_.flatten(value));
memo.push(value);
return memo;
- });
+ }, []);
};
// Return a version of the array that does not contain the specified value(s).
@@ -293,10 +299,10 @@
// Produce a duplicate-free version of the array. If the array has already
// been sorted, you have the option of using a faster algorithm.
_.uniq = function(array, isSorted) {
- return _.reduce(array, [], function(memo, el, i) {
+ return _.reduce(array, function(memo, el, i) {
if (0 == i || (isSorted === true ? _.last(memo) != el : !_.include(memo, el))) memo.push(el);
return memo;
- });
+ }, []);
};
// Produce an array that contains every item shared between all the