按键计数数组对象的频率答案

【问题标题】：Count frequency of array objects by key按键计数数组对象的频率
【发布时间】：2020-09-07 12:07:18
【问题描述】：

我有很多这样的学生：

    var school =[ 
    {
    class: "ss1",
    student: "J. Kent",
    scores: "accurate"
},
{
    class: "ss1",
    student: "P. Ben",
    scores: "accurate"
},
{
    class: "ss3",
    student: "T. Maddison",
    scores: "error"
},
{
    class: "jss1",
    student: "R Briggs",
    scores: "accurate"
},
{
    class: "ss1",
    student: "P. Roberts",
    scores: "accurate"
},
{
    class: "ss1",
    student: "A. Minder",
    scores: "error"
},
{
    class: "ss1",
    student: "C. Trust",
    scores: "accurate"
},

]

我想计算属于 class: "ss1" scores: "accurate" 的某人出现的次数。我四处寻找图书馆以使这变得容易，但无法获得。欢迎任何方法或更简单的方法。

【问题讨论】：

标签： javascript arrays sorting filter

【解决方案1】：

您可以使用Array.filter() 过滤值并获取其长度。

var school=[{class:"ss1",student:"J. Kent",scores:"accurate"},{class:"ss1",student:"P. Ben",scores:"accurate"},{class:"ss3",student:"T. Maddison",scores:"error"},{class:"jss1",student:"R Briggs",scores:"accurate"},{class:"ss1",student:"P. Roberts",scores:"accurate"},{class:"ss1",student:"A. Minder",scores:"error"},{class:"ss1",student:"C. Trust",scores:"accurate"}];

console.log(school.filter(scl => scl.class === 'ss1' && scl.scores === 'accurate').length)

【讨论】：

【解决方案2】：

您可以使用array.filter()

const school = [
  {
    class: "ss1",
    student: "J. Kent",
    scores: "accurate",
  },
  {
    class: "ss1",
    student: "P. Ben",
    scores: "accurate",
  },
  {
    class: "ss3",
    student: "T. Maddison",
    scores: "error",
  },
  {
    class: "jss1",
    student: "R Briggs",
    scores: "accurate",
  },
  {
    class: "ss1",
    student: "P. Roberts",
    scores: "accurate",
  },
  {
    class: "ss1",
    student: "A. Minder",
    scores: "error",
  },
  {
    class: "ss1",
    student: "C. Trust",
    scores: "accurate",
  },
];


const getResults = (group, score) => {
  return school.filter((obj) => obj.class === group && obj.scores === score).length;
}

const result = getResults("ss1", "accurate");

console.log(result);

或array.reduce()

const school = [
  {
    class: "ss1",
    student: "J. Kent",
    scores: "accurate",
  },
  {
    class: "ss1",
    student: "P. Ben",
    scores: "accurate",
  },
  {
    class: "ss3",
    student: "T. Maddison",
    scores: "error",
  },
  {
    class: "jss1",
    student: "R Briggs",
    scores: "accurate",
  },
  {
    class: "ss1",
    student: "P. Roberts",
    scores: "accurate",
  },
  {
    class: "ss1",
    student: "A. Minder",
    scores: "error",
  },
  {
    class: "ss1",
    student: "C. Trust",
    scores: "accurate",
  },
];


const getResults = (group, score) => {
  return school.reduce((count, obj) => obj.class === group && obj.scores === score ? ++count : count, 0);
}

const result = getResults("ss1", "accurate");

console.log(result);

【讨论】：