将Javascript数组简化为映射并删除重复的值 [英] Reducing Javascript array into a map and removing duplicate values

问题描述

我敢肯定有一个干净的方法可以做到这一点，但是我不知道该怎么做.我想拔出一列，以便只返回值的第一次出现，但我想保留它附带的键.

I am sure there is a clean way to do this, but I have no idea how to do it. I want to pluck a column out such that I am only returning the first occurrence of a value, but I want to keep the key that went with it.

我有一个要减少的数据集.我想拔出悬崖".

I have a dataset that I want reduced. I want to pluck out the 'precip'.

说我有这个:

[
  "2019-01-01" => {"temp" : "cold", "season" : "winter", "precip" : "snow"},
  "2019-02-01" => {"temp" : "cold", "season" : "winter", "precip" : "none"},
  "2019-03-01" => {"temp" : "mild", "season" : "spring", "precip" : "rain"},
  "2019-04-01" => {"temp" : "mild", "season" : "spring", "precip" : "none"},
  "2019-05-01" => {"temp" : "warm", "season" : "spring", "precip" : "rain"},
  "2019-06-01" => {"temp" : "warm", "season" : "summer", "precip" : "hail"},
  "2019-07-01" => {"temp" : "hot", "season" : "summer", "precip" : "none"}
]

我想以此结尾:

[
  "2019-01-01" => "snow",
  "2019-02-01" => "none",
  "2019-03-01" => "rain",
  "2019-06-01" => "hail"
]

我认为Array.map与此有关，但是我不知道如何返回键/值对，而不仅仅是返回一个值(即map(function(d) { return d.precip }))

I would think that Array.map has something to do with this, but I don't know how to return the key/value pair instead of just a value (i.e. map(function(d) { return d.precip }) )

实现此目的的流畅方法是什么?

What is the smooth way to do this?

谢谢.

推荐答案

您可以创建 Map ，并仅获取具有相同键的第一项.

You could create a Map and take only the first item with the same key.

function getFirstPrecip(data) {
    return Object.assign({}, ...Array.from(
        data.reduce((m, o) => {
            var [[k, { precip }]] = Object.entries(o);
            return m.has(precip) ? m : m.set(precip, k);
        }, new Map),
        ([k, v]) => ({ [v]: k })
    ));
}

var data = [{ "2019-01-01": { temp: "cold", season: "winter", precip: "snow" } }, { "2019-02-01": { temp: "cold", season: "winter", precip: "none" } }, { "2019-03-01": { temp: "mild", season: "spring", precip: "rain" } }, { "2019-04-01": { temp: "mild", season: "spring", precip: "none" } }, { "2019-05-01": { temp: "warm", season: "spring", precip: "rain" } }, { "2019-06-01": { temp: "warm", season: "summer", precip: "hail" } }, { "2019-07-01": { temp: "hot", season: "summer", precip: "none" } }];

console.log(getFirstPrecip(data));

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