回答編集履歴
4
オブジェクト初期化子 \+ Object\.entries \(ES8\)
answer
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@@ -52,6 +52,35 @@
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console.log(JSON.stringify(results)); // [{"name":"abc","value":223},{"name":"def","value":51},{"name":"hij","value":789}]
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```
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### オブジェクト初期化子 + Object.entries (ES8)
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先行仕様(ES8/ES2017)ですが、`Object.entries` を利用するとオブジェクト初期化子のコードを更にエレガントに書けます。
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`Object.entries` は Polyfill コードがあるので、現行でも使おうと思えば使えます。
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- [19.1.2.17 Object.entries - ECMAScript® 2017 Language Specification](https://tc39.github.io/ecma262/#sec-object.entries)
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- [Object.entries() - JavaScript | MDN](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object/entries)
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```JavaScript
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'use strict';
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var src = [{'name':'abc','value':100},{'name':'def','value':50},{'name':'abc','value':123},{'name':'hij','value':789},{'name':'def','value':1}];
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var results = Object.entries(src.reduce((object, current) => {
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var name = current.name;
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if (object.hasOwnProperty(name)) {
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object[name] += current.value;
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} else {
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object[name] = current.value;
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}
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return object;
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}, {})).map(entry=>{
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return {name: entry[0], value: entry[1]};
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});
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console.log(JSON.stringify(results)); // [[{"name":"abc","value":223},{"name":"def","value":51},{"name":"hij","value":789}]
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```
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### new Map (ES6)
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オブジェクト初期化子で「`name` が `String` 型でなければならない」欠点を `new Map` で克服しており、可搬性が最も高いと思われます。
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@@ -81,5 +110,6 @@
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- 2016/12/28 00:08 new Mapコードを Object.keys -> Map#forEach
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- 2016/12/28 00:32 new Mapコードを三項演算子を使ったコードに修正
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- 2016/12/28 01:38 オブジェクト初期化子 + Object.entriesのコード追記
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Re: stakezaki さん
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3
new Mapコードを三項演算子を使ったコードに修正
answer
CHANGED
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@@ -66,11 +66,7 @@
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src.reduce(function (map, current) {
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var name = current.name;
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if (map.has(name)) {
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-
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map.set(name, map.has(name) ? map.get(name) + current.value : current.value);
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} else {
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map.set(name, current.value);
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}
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return map;
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}, map).forEach(function (value, key, map) {
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@@ -83,6 +79,7 @@
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### 更新履歴
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- 2016/12/28 00:08 new Mapコードを Object.keys -> Map#forEach
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-
- 2016/12/28 00:
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- 2016/12/28 00:32 new Mapコードを三項演算子を使ったコードに修正
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Re: stakezaki さん
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2
Map#forEach を使ったコードに修正
answer
CHANGED
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@@ -59,9 +59,11 @@
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```JavaScript
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'use strict';
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var src = [{'name':'abc','value':100},{'name':'def','value':50},{'name':'abc','value':123},{'name':'hij','value':789},{'name':'def','value':1}]
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var src = [{'name':'abc','value':100},{'name':'def','value':50},{'name':'abc','value':123},{'name':'hij','value':789},{'name':'def','value':1}],
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map = new Map,
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results = [];
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-
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src.reduce(function (map, current) {
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var name = current.name;
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if (map.has(name)) {
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@@ -71,14 +73,16 @@
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}
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return map;
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}, map).forEach(function (value, key, map) {
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this.push({name: key, value: value});
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},
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}, results);
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var results = [...map.entries()].map(function (entry) {
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return {name: entry[0], value: entry[1]};
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});
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console.log(JSON.stringify(results)); // [[{"name":"abc","value":223},{"name":"def","value":51},{"name":"hij","value":789}]
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console.log(JSON.stringify([...map.entries()])); // [["abc",223],["def",51],["hij",789]]
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```
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84
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### 更新履歴
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85
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+
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86
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- 2016/12/28 00:08 ES6版を Map#forEach を使ったコードに修正
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87
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Re: stakezaki さん
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1
typo修正
answer
CHANGED
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File without changes
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