JS（ES6）：根据对象属性简化数组

Question

我有一个像这样的数组：

const fruits = [ 
    { fruit: 'apple',  year: 2018 },
    { fruit: 'apple',  year: 2018 },
    { fruit: 'banana', year: 2018 },
    { fruit: 'orange', year: 2018 },
    { fruit: 'apple',  year: 2017 },
    { fruit: 'apple',  year: 2016 }
];

现在，我想简化此数组，以查看每年有多少个水果，总数是多少。 这样结果看起来像这样：

const result = [ 
    { year: 2018, apple: 2, banana: 1, orange: 1 total: 4 },
    { year: 2017, apple: 1, total: 1 },
    { year: 2016, apple: 1, total: 1 }
];

我曾尝试使用reduce，但是我不知道如何根据年份对它进行分组。 也许还有lodash的助手？

Answer 1

使用Object.values并reduce

var output = Object.values(fruits.reduce( (a,c) => {
  a[c.year] = a[c.year] || { year : c.year };  
  a[c.year]["total"] = (a[c.year]["total"] || 0) + 1;
  a[c.year][c.fruit] = (a[c.year][c.fruit] || 0) + 1;
  return a;
},{}));

演示版

 var fruits = [{ fruit: 'apple', year: 2018 }, { fruit: 'apple', year: 2018 }, { fruit: 'banana', year: 2018 }, { fruit: 'orange', year: 2018 }, { fruit: 'apple', year: 2017 }, { fruit: 'apple', year: 2016 } ]; var output = Object.values(fruits.reduce((a, c) => { a[c.year] = a[c.year] || { year: c.year }; a[c.year]["total"] = (a[c.year]["total"] || 0) + 1; a[c.year][c.fruit] = (a[c.year][c.fruit] || 0) + 1; return a; }, {})); console.log(output); 

Answer 2

您可以使用array#reduce根据年份对数据进行分组，并在对象累加器中计算水果的出现次数。 然后使用Object.values()从该对象获取所有值

 const fruits = [ { fruit: 'apple', year: 2018 }, { fruit: 'apple', year: 2018 }, { fruit: 'banana', year: 2018 }, { fruit: 'orange', year: 2018 }, { fruit: 'apple', year: 2017 }, { fruit: 'apple', year: 2016 } ], result = Object.values(fruits.reduce((r,{fruit, year}) => { r[year] = r[year] || {year}; r[year][fruit] = (r[year][fruit] || 0) + 1; r[year]['total'] = (r[year]['total'] || 0) + 1; return r; },{})); console.log(result); 

Answer 3

您可以使用数组作为结果集，以保持年份的给定顺序。

 var fruits = [{ fruit: 'apple', year: 2018 }, { fruit: 'apple', year: 2018 }, { fruit: 'banana', year: 2018 }, { fruit: 'orange', year: 2018 }, { fruit: 'apple', year: 2017 }, { fruit: 'apple', year: 2016 }], result = fruits.reduce((r, { year, fruit }) => { var item = r.find(o => o.year === year); if (!item) { r.push(item = { year }); } item[fruit] = (item[fruit] || 0) + 1; return r; }, []); console.log(result); 

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