对数组值进行分组并添加属性答案

【问题标题】：Group array values and add properties对数组值进行分组并添加属性
【发布时间】：2020-10-02 02:29:39
【问题描述】：

有谁知道通过对象键对对象数组进行分组的方法？例如，我有许多汽车对象：

const cars = [
  "fiat-palio", 
  "fiat-stilo", 
  "fiat-strada", 
  "fiat-uno", 
  "fiat-uno", 
  "gm-corsa", 
  "gm-celta", 
  "ford-fiesta", 
  "volkswagen-gol", 
  "volkswagen-gol", 
  "volkswagen-gol", 
  "volkswagen-voyage"
]

我想创建一个新的汽车对象数组，按每个汽车制造商分组：

{ 
  "fiat": { 
    "palio": 1, 
    "stilo": 1, 
    "strada": 1, 
    "uno": 2 
  }, 
  "gm": { 
    "corsa": 1, 
    "celta": 1 
  }, 
  "ford": { 
    "fiesta": 1 
  }, 
  "volkswagen": { 
    "gol": 3, 
    "voyage": 1 
  }
}

【问题讨论】：

你尝试过什么来达到你想要的结果？

标签： javascript arrays object grouping

【解决方案1】：

您可以拆分每辆汽车并破坏阵列以获取品牌和型号。确定这些值后，只需将这些值分散到 reducer 中即可。

const cars = [
  "fiat-palio", "fiat-stilo", "fiat-strada", "fiat-uno", "fiat-uno", 
  "gm-corsa",  "gm-celta", 
  "ford-fiesta", 
  "volkswagen-gol", "volkswagen-gol", "volkswagen-gol", "volkswagen-voyage"
];

const frequency = cars.reduce((groups, car) => ({
  ...groups,
  ...(([make, model]) => ({
    [make] : {
      ...groups?.[make],
      [model] : (groups?.[make]?.[model] || 0) + 1
    }
  }))(car.split('-'))
}), {});

console.log(frequency);

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

代码高尔夫乐趣

f=l=>l.reduce((g,c)=>({...g,...(([m,n])=>({[m]:{...g?.[m],[n]:(g?.[m]?.[n]||0)+1}}))(c.split('-'))}),{})（104 字节）

用法：只需将cars 传递给上面的f 函数即可。

【讨论】：

【解决方案2】：

您可以使用数组的reduce方法来产生所需的输出。

reduce 在每次迭代中获取数组先前和当前项并返回标量值。 here the documentation

const cars = [
  "fiat-palio", 
  "fiat-stilo", 
  "fiat-strada", 
  "fiat-uno", 
  "fiat-uno", 
  "gm-corsa", 
  "gm-celta", 
  "ford-fiesta", 
  "volkswagen-gol", 
  "volkswagen-gol", 
  "volkswagen-gol", 
  "volkswagen-voyage"
];

let result = cars.reduce((obj, item) => {
  let pair = item.split('-'); // split key and value
  let mark = pair[0]; 
  let model = pair[1];

  if(!obj.hasOwnProperty(mark)) { // initialize new mark and model
     obj[mark] = {};
     obj[mark][model] = 1;
  } else {
    if(obj[mark].hasOwnProperty(model)) { // increment existing model 
      obj[mark][model] += 1; 
    } else { // initialize model of existing mark
       obj[mark][model] = 1;
    }
  }

  return obj;
}, {}) 


console.log(result)

【讨论】：