Question

我有一个类似这样的JavaScript数组：

var items = [
 { id:1, group:'Produce', name:'Apple', weight: 0.5 },
 { id:2, group:'Produce', name:'Banana', weight: 0.2 },
 { id:3, group:'Meat', name:'Beef', weight: 1.0 },
 { id:4, group:'Meat', name:'Chicken', weight: 0.75 },
 { id:5, group:'Dairy', name:'Milk', weight:1.0 }
];

我想查看这个数组，然后通过它们的组动态地将它们放入数组中。我尝试了以下操作，但它没有用：

var groups = [];
for (var i = 0; i<items.length; i++) {
  var groupName = items[i].group;
  if (groups.includes(groupName) === false) {
    groups[groupName] = new Array();
  }
  groups[groupName].push(items[i]);
}

基本上，我正在尝试在JavaScript中创建一个Hashtable。关键是组名称，值为该组中项目的Array。但是，我没有成功。我在这里缺少什么？

非常感谢你的帮助！

Answer 1

我建议您遵循简单的解决方案。

＆＃13;

var items = [
 { id:1, group:'Produce', name:'Apple', weight: 0.5 },
 { id:2, group:'Produce', name:'Banana', weight: 0.2 },
 { id:3, group:'Meat', name:'Beef', weight: 1.0 },
 { id:4, group:'Meat', name:'Chicken', weight: 0.75 },
 { id:5, group:'Dairy', name:'Milk', weight:1.0 }
], obj = {};

items.forEach(c => (obj[c.group] || (obj[c.group] = [])).push(c));

console.log(obj);

＆＃13;

Answer 2

您的groups应该是一个对象。

然后你正在测试groups.includes(groupName)，但它是an array function，而你正在创建一个哈希表。

而是使用groups[groupName] === undefined检查对象上是否存在密钥。

var groups = {};
for (var i = 0; i<items.length; i++) {
  var groupName = items[i].group;
  if (groups[groupName] === undefined) {
    groups[groupName] = new Array();
  }
  groups[groupName].push(items[i]);
}

Answer 3

您只能使用一个对象并检查密钥是否存在。如果不采取新阵列。

var items = [{ id: 1, group: 'Produce', name: 'Apple', weight: 0.5 }, { id: 2, group: 'Produce', name: 'Banana', weight: 0.2 }, { id: 3, group: 'Meat', name: 'Beef', weight: 1.0 }, { id: 4, group: 'Meat', name: 'Chicken', weight: 0.75 }, { id: 5, group: 'Dairy', name: 'Milk', weight:1.0 }],
    groups = Object.create(null),          // take a really empty object
    groupName,
    i;
    
for (i = 0; i < items.length; i++) {
    groupName = items[i].group;
    if (!groups[groupName]) {              // check if the key in object exists
        groups[groupName] = [];            // if not, assign an empty array
    }
    groups[groupName].push(items[i]);
}

console.log(groups);

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Answer 4

另一种选择是使用reduce：

＆＃13;

var items = [
 { id:1, group:'Produce', name:'Apple', weight: 0.5 },
 { id:2, group:'Produce', name:'Banana', weight: 0.2 },
 { id:3, group:'Meat', name:'Beef', weight: 1.0 },
 { id:4, group:'Meat', name:'Chicken', weight: 0.75 },
 { id:5, group:'Dairy', name:'Milk', weight:1.0 }
];

const grouped = items.reduce((accum, item) => {
	accum[item.group] = accum[item.group] ? accum[item.group].concat(item) : [item];
	return accum;
}, {});

console.log(grouped);

＆＃13;

Answer 5

我alusty使用lodash或下划线

但是，请尝试使用reduce函数

 var items = [
   { id:1, group:'Produce', name:'Apple', weight: 0.5 },
     { id:2, group:'Produce', name:'Banana', weight: 0.2 },
     { id:3, group:'Meat', name:'Beef', weight: 1.0 },
     { id:4, group:'Meat', name:'Chicken', weight: 0.75 },
     { id:5, group:'Dairy', name:'Milk', weight:1.0 }
 ];

 Array.prototype.groupDynamically = function(prop) {
   return this.reduce(function(groups, item) {
     var val = item[prop];
     groups[val] = groups[val] || [];
     groups[val].push(item);
     return groups;
   }, {});
 }

 //Then in your case say

var groups = items.groupDynamically('group');

JavaScript - 将项目分组到数组中

5 个答案: