显示对象数组中的项目数而不重复答案

【问题标题】：Display number of items from array of objects without duplicate显示对象数组中的项目数而不重复
【发布时间】：2020-10-06 09:41:06
【问题描述】：

我正在学习 javascript，但遇到了一些问题。我想迭代一个对象数组，但有一些“选项”：

不显示重复项。
显示项目数。

预期结果：

received 1

missed 2

dialed 3

我知道如何迭代一个对象数组并使用.length 显示每个项目的数量，但我不知道迭代+显示数量+删除重复项...你能帮我吗？

const calls = [
  {
    type: "missed",
    date: "xx-xx-xx"
  },
  {
    type: "received",
    date: "xx-xx-xx"
  },
  {
    type: "dialed",
    date: "xx-xx-xx"
  },
  {
    type: "missed",
    date: "xx-xx-xx"
  },
  {
    type: "dialed",
    date: "xx-xx-xx"
  },
  {
    type: "dialed",
    date: "xx-xx-xx"
  }
];

【问题讨论】：

标签： javascript arrays loops object duplicates

【解决方案1】：

一个很好的分组项目的方法是使用reduce（它也很灵活，所以如果你添加其他类型也没有问题）：

const calls = [{
    type: "missed",
    date: "xx-xx-xx"
  },
  {
    type: "received",
    date: "xx-xx-xx"
  },
  {
    type: "dialed",
    date: "xx-xx-xx"
  },
  {
    type: "missed",
    date: "xx-xx-xx"
  },
  {
    type: "dialed",
    date: "xx-xx-xx"
  },
  {
    type: "dialed",
    date: "xx-xx-xx"
  }
];

const output = calls.reduce((aggObj, item) => {
    if(!aggObj[item.type]){
        aggObj[item.type] = 0
    }
    aggObj[item.type] += 1;
    return aggObj;
}, {});
//output as object:
console.log(output);

//output as array:
const outArr = Object.entries(output);
console.log(outArr);

//output as strings:
outArr.forEach(([k,v]) => console.log(k,v));

【讨论】：

【解决方案2】：

const calls = [{
    type: "missed",
    date: "xx-xx-xx"
  },
  {
    type: "received",
    date: "xx-xx-xx"
  },
  {
    type: "dialed",
    date: "xx-xx-xx"
  },
  {
    type: "missed",
    date: "xx-xx-xx"
  },
  {
    type: "dialed",
    date: "xx-xx-xx"
  },
  {
    type: "dialed",
    date: "xx-xx-xx"
  }
];
const types = ["missed", "received", "dialed"];
types.forEach(type => {
  console.log(type + ": " + calls.filter((calls) => calls.type === type).length);
});

【讨论】：

【解决方案3】：

希望对你有帮助

var newArr = calls.filter((x, index, self) =>
  index === self.findIndex((t) => (
    t.type === x.type && t.date === x.date)));

console.log(newArr);

【讨论】：