如何在javascript中的对象数组下获取值重复的计数

Question

I have an array which have some repetition count. I want to get the count of that repetition. My array is like this:

var array = [
    { asset: "A", sector: "Hospital" },
    { asset: "B", sector: "Hardware" },
    { asset: "C", sector: "Networking" },
    { asset: "D", sector: "Networking" },
    { asset: "E", sector: "Food" },
    { asset: "F", sector: "Hospital" },
    { asset: "G", sector: "Hardware" },
    { asset: "H", sector: "Industrial" },
    { asset: "I", sector: "Transport" },
    { asset: "J", sector: "Hardware" },
    { asset: "K", sector: "Networking" },
    { asset: "L", sector: "Transport" }
]

Now I want the Repetition count something like this also in sorted order like this:

final_array = [
    { sector: 'Hardware', count: 3 },
    { sector: 'Networking', count: 3 },
    { sector: 'Hospital', count: 2 },
    { sector: 'Transport', count: 2 },
    { sector: 'Food', count: 1 },
    { sector: 'Industrial', count: 1 }
]

I don't get the clue from where can do this. I got many link but they solve the repetition under array not on Array of objects.

I use the one approach but that not solve my issue

var finalD = [];
c.forEach(x => {
    if (isSectorExists(x.sector, finalD) == true) {
        //Here I don't know how I will increase the counter.
    } else {
        finalD.push({ sector: x.sector, count: 1 });
    }
});

var isSectorExists = (sector, arr) => {
    return arr.some(function(el) {
        return el.sector === sector;
    });
};

I know that my approach was very long. Is someone have the best and easy approach for doing this kind of task. Any Help is really Appreciated. Thanks in Advance

Answer 1

You can build an object counts with sector name as keys and an object that stores counts as values, iterate through your array and update those counts, and then finally get the values of that counts object.

 var array = [ { asset: "A", sector: "Hospital" }, { asset: "B", sector: "Hardware" }, { asset: "C", sector: "Networking" }, { asset: "D", sector: "Networking" }, { asset: "E", sector: "Food" }, { asset: "F", sector: "Hospital" }, { asset: "G", sector: "Hardware" }, { asset: "H", sector: "Industrial" }, { asset: "I", sector: "Transport" }, { asset: "J", sector: "Hardware" }, { asset: "K", sector: "Networking" }, { asset: "L", sector: "Transport" } ]; var counts = array.reduce((m, c) => { if (c.sector in m) m[c.sector].count += 1; else m[c.sector] = { sector: c.sector, count: 1}; return m; }, {}); let finalArray = Object.values(counts).sort((a, b) => b.count - a.count); console.log(finalArray);

This will get the counts in linear time (as opposed to calling isSectorExists for every element which would make it O(n^2) .