demo for reduce

reduce.js

@@ -0,0 +1,104 @@
+var async = require('async');
+
+var t = require('./t');
+var log = t.log;
+
+/**
+ * Reduce可以让我们给定一个初始值，用它与集合中的每一个元素做运算，最后得到一个值。reduce从左向右来遍历元素，如果想从右向左，可使用reduceRight。
+ */
+//reduce(arr, memo, iterator(memo,item,callback), callback(err,result))
+//alias: inject, foldl
+
+var arr = [1,3,5];
+
+async.reduce(arr, 100, function(memo, item, callback) {
+    log('1.1 enter: ' + memo +', ' + item);
+    setTimeout(function() {
+        callback(null, memo+item);
+    }, 100);
+},function(err, result) {
+    log('1.1 err: ', err);
+    log('1.1 result: ', result);
+});
+// 28.789> 1.1 enter: 100, 1
+// 28.889> 1.1 enter: 101, 3
+// 28.999> 1.1 enter: 104, 5
+// 29.109> 1.1 err:
+// 29.109> 1.1 result: 109
+
+async.reduce(arr, 100, function(memo, item, callback) {
+    log('1.2 enter: ' + memo +', ' + item);
+    setTimeout(function() {
+        if(item===3) callback('myerr');
+        else callback(null, memo+item);
+    }, 100);
+},function(err, result) {
+    log('1.2 err: ', err);
+    log('1.2 result: ', result);
+});
+// 05.541> 1.2 enter: 100, 1
+// 05.649> 1.2 enter: 101, 3
+// 05.760> 1.2 err: myerr
+// 05.760> 1.2 result:
+
+//alias: foldr
+async.reduceRight(arr, 100, function(memo, item, callback) {
+    log('1.3 enter: ' + memo +', ' + item);
+    setTimeout(function() {
+        callback(null, memo+item);
+    }, 100);
+},function(err, result) {
+    log('1.3 err: ', err);
+    log('1.3 result: ', result);
+});
+// 28.789> 1.3 enter: 100, 5
+// 28.889> 1.3 enter: 105, 3
+// 28.999> 1.3 enter: 108, 1
+// 29.109> 1.3 err:
+// 29.109> 1.3 result: 109
+
+//
+async.reduce(arr, 100, function(memo,item,callback) {
+    log('1.4 enter: '+memo+','+item);
+    t.inc(item, function(err,n) {
+        log('1.4 handle: ',n);
+        callback(null, memo+n);
+    });
+}, function(err,result) {
+    log('1.4 err: ', err);
+    log('1.4 result: ', result);
+});
+// 28.789> 1.4 enter: 100,1
+// 28.999> 1.4 handle: 2
+// 28.999> 1.4 enter: 102,3
+// 29.209> 1.4 handle: 4
+// 29.209> 1.4 enter: 106,5
+// 29.409> 1.4 handle: 6
+// 29.409> 1.4 err:
+// 29.409> 1.4 result: 112
+// --> spent 0.62s
+
+async.map(arr, function(item, callback) {
+    log('1.5 enter: ', item);
+    t.inc(item, function(err,n){
+        log('1.5 handle: ', n);
+        callback(null,n);
+    });  
+},function(err, results) {
+    log('1.5 err: ', err);
+    log('1.5 results: ', results);
+    var sum = results.reduce(function(memo, item) {
+        return memo + item;
+    }, 100);
+    log('1.5 sum: ', sum);
+});
+// 28.789> 1.5 enter: 1
+// 28.789> 1.5 enter: 3
+// 28.789> 1.5 enter: 5
+// 28.999> 1.5 handle: 2
+// 28.999> 1.5 handle: 4
+// 28.999> 1.5 handle: 6
+// 28.999> 1.5 err:
+// 28.999> 1.5 results: [ 2, 4, 6 ]
+// 28.999> 1.5 sum: 112
+// --> spent 0.21