JavaScript-如何计算JSON中的每个键值？

Question

JavaScript - How to count each key value in JSON?

[
  {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}
]

with this JSON format to:

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

or

ultimately, to:

[
  {date: "2017-09-26", dot_count: 1, line_count: 0},
  {date: "2017-09-28", dot_count: 1, line_count: 2}
]

Answer 1

You could use a hash table and create a new object if the hash does not exists. Later add the count value to the group.

 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); 

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Answer 2

You are probably looking for 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;
}, []);

for your second level question you probably want to pair array.prototype.map with 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}
    ];
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);