javascript - 如何在javascript中分组并检测是否存在

Question

我想每天检测此输入中是否存在特定代码:

const arrayA = [
{"date":"2018/9/10", "code":"A"},
{"date":"2018/9/10", "code":"B"},
{"date":"2018/9/10", "code":"C"},
{"date":"2018/9/10", "code":"A"},
{"date":"2018/9/11", "code":"A"},
{"date":"2018/9/11", "code":"C"}];

规则:如果当天有 B，则我们添加 X如果当天有 C，那么我们添加 Y如果 B & C 在我们添加 Y 的那一天出现

我在使用过滤器和 .some 的代码中迷失了自己...

预期输出

   const arrayOut = [
    {"date":"2018/9/10", "code":"A"},
    {"date":"2018/9/10", "code":"B"},
    {"date":"2018/9/10", "code":"C"},
    {"date":"2018/9/10", "code":"A"},
    {"date":"2018/9/10", "code":"Y"},
    {"date":"2018/9/11", "code":"A"},
    {"date":"2018/9/11", "code":"B"},
    {"date":"2018/9/11", "code":"X"}];

const arrayA = [
{"date":"2018/9/10", "code":"A"},
{"date":"2018/9/10", "code":"B"},
{"date":"2018/9/10", "code":"C"},
{"date":"2018/9/10", "code":"A"},
{"date":"2018/9/11", "code":"B"},
{"date":"2018/9/11", "code":"B"}];

var helper = [];
arrayA.map ( e => {
  var key = e.date;
  if(!helper[key]){
     helper.push(key);
     var arr = arrayA.filter(e => e.date == key && (e.code == "B" || e.code == "C"));

      if(arr.length > 0) console.log("act is here");
      else console.log("act not here");
	}
  
  });

Answer 1

我个人会将它映射到一个对象，这样您就可以进行简单的 bool 检查，而不仅仅是将该项目附加到列表中。

const arrayA = [
{"date":"2018/9/10", "code":"A"},
{"date":"2018/9/10", "code":"B"},
{"date":"2018/9/10", "code":"C"},
{"date":"2018/9/10", "code":"A"},
{"date":"2018/9/11", "code":"B"},
{"date":"2018/9/11", "code":"B"}];

const state = arrayA.reduce( (obj, state) => {
  obj[state.date] = obj[state.date] || {}
  obj[state.date][state.code] = true
  return obj
}, {});

Object.entries(state).forEach(([date, codes]) => {
  if (codes.C) {
    arrayA.push({ date, code: 'Y' })
  } else if (codes.B) {
    arrayA.push({ date, code: 'X' })
  }
})

console.log(arrayA)

---

在没有 Object.entries() 的情况下更新为相同的方法:

const arrayA = [
{"date":"2018/9/10", "code":"A"},
{"date":"2018/9/10", "code":"B"},
{"date":"2018/9/10", "code":"C"},
{"date":"2018/9/10", "code":"A"},
{"date":"2018/9/11", "code":"B"},
{"date":"2018/9/11", "code":"B"}];

const state = arrayA.reduce( (obj, state) => {
  obj[state.date] = obj[state.date] || {}
  obj[state.date][state.code] = true
  return obj
}, {});

for (date in state)
{
  if (state[date].C)
    arrayA.push({ date, code: 'Y' });
  else if (state[date].B)
    arrayA.push({ date, code: 'X' });
}

console.log(arrayA);