Question

JavaScript - 如何计算JSON中的每个键值？

header('Content-Type: application/json');

使用此JSON格式：

[
  {date: "2017-09-28", type: "line", count: 1},
  {date: "2017-09-28", type: "line", count: 1},
  {date: "2017-09-28", type: "dot", count: 1},
  {date: "2017-09-26", type: "dot", count: 1}
]

或

最终，到：

[
  {date: "2017-09-26", count: 1},
  {date: "2017-09-28", count: 3}
]

Answer 1

如果哈希不存在，您可以使用哈希表并创建新对象。稍后将计数值添加到组中。

＆＃13;

var data = [{ date: "2017-09-28", type: "line", count: 1 }, { date: "2017-09-28", type: "line", count: 1 }, { date: "2017-09-28", type: "dot", count: 1 }, { date: "2017-09-26", type: "dot", count: 1 }],
    hash = Object.create(null),
    result = [];
    
data.forEach(function (o) {
    if (!hash[o.date]) {
        hash[o.date] = { date: o.date,  dot_count: 0, line_count: 0 };
        result.push(hash[o.date]);
    }
    hash[o.date][o.type + '_count'] += o.count;
});

result.sort(function (a, b) { return a.date.localeCompare(b.date); });

console.log(result);

＆＃13;

.as-console-wrapper { max-height: 100% !important; top: 0; }

＆＃13;

Answer 2

您可能正在寻找array.prototype.reduce。

const test = [
  {date: "2017-09-28", type: "line", count: 1},
  {date: "2017-09-28", type: "line", count: 1},
  {date: "2017-09-28", type: "dot", count: 1},
  {date: "2017-09-26", type: "dot", count: 1}
];
let result = test.reduce((group, current) => {
    let index = group.findIndex(ele => ele.date === current.date);
    if (index === -1) {
        group.push(current);
        return group;
    } 
    group[index].count += current.count;
    return group;
}, []);

对于您的第二级问题，您可能希望将array.prototype.map与reduce配对。

const test = [
      {date: "2017-09-28", type: "line", count: 1},
      {date: "2017-09-28", type: "line", count: 1},
      {date: "2017-09-28", type: "dot", count: 1},
      {date: "2017-09-26", type: "dot", count: 1}
    ];
const mapper = item => ({ 
    date: item.date, 
    dot_count: (item.type === 'dot') ? 1 : 0,
    line_count: (item.type === 'line') ? 1 : 0,
    total_count: item.count,
});
const reducer = (group, current) => {
    let index = group.findIndex(ele => ele.date === current.date);
    if (index === -1) {
        group.push(current);
        return group;
    } 
    group[index] = { 
        ...group[index], 
        dot_count: group[index].dot_count + current.dot_count,
        line_count: group[index].line_count + current.line_count,
        total_count: group[index].total_count + current.total_count,
    };
    return group;
};
let result = test.map(mapper).reduce(reducer, []);
console.log(result);

JavaScript - 如何计算JSON中的每个键值？

2 个答案: