javascript 对象数组通过特定键值获取 uniq 值

Question

I have bar like:

Server returns:

const rows = [
 {type: "global", count: 6, name: "Name", orderliness: 1},
 {type: "global", count: 5, name: "Name", orderliness: 2},
 {type: "local", count: 1, name: "Name", orderliness: 3},
 {type: "global", count: 8, name: "Name", orderliness: 3},
 {type: "local", count: 2, name: "Name", orderliness: 1},
]

And I should get not repeated orderliness and get output:

[
 {type: "global", count: 5, name: "Name", orderliness: 2}
]

And push no repeated item to rows like:

const rows = [
 {type: "global", count: 6, name: "Name", orderliness: 1},
 {type: "global", count: 5, name: "Name", orderliness: 2},
 {type: "local", count: 1, name: "Name", orderliness: 3},
 {type: "global", count: 8, name: "Name", orderliness: 3},
 {type: "local", count: 2, name: "Name", orderliness: 1},
 // this item I pushed
 {type: "local", count: 0, name: "Name", orderliness: 2},
]

I tried do like:

function getUnique(arr, comp) {
    return (
        arr
            .map((e) => e[comp])
            // store the keys of the unique objects
            .map((e, i, final) => final.indexOf(e) === i && i)
            // eliminate the dead keys & store unique objects
            .filter((e) => arr[e])
            .map((e) => arr[e])
    );
}
getUnique(rows, 'orderliness');

But it returns like:

[
 {type: "global", count: 6, name: "Name", orderliness: 1},
 {type: "global", count: 5, name: "Name", orderliness: 2},
 {type: "local", count: 1, name: "Name", orderliness: 3},
]

Answer 1

So you have an array with rows where entries are of one of two types ( "global" and "local" ), and you're trying to find rows that only have one type and not the other then, having found them, push new rows for for the "other" type into rows with count set to 0.

Here's how I'd do it (see comments).

For getUnique :

function getUnique(arr, comp) {
    // Get a count of matching objects
    const counts = new Map();
    for (const {[comp]: value} of arr) {
        const count = counts.get(value) || 0; // `get` returns `undefined` if it's
                                              // not there; we replace that with 0
        counts.set(value, count + 1);
    }
    // Return only the unique ones
    return arr.filter(({[comp]: value}) => counts.get(value) === 1);
}

That makes two passes through the array rather than four, taking advantage of Map's binary tree or similar sublinear lookup time.

Then to add the rows:

// Get the unique rows, create new rows for the "other"
// type with count = 0 and push them into `rows`
rows.push(...getUnique(rows, 'orderliness').map(entry => ({
    ...entry,
    type: entry.type === "global" ? "local" : "global",
    count: 0
})));

Live Example:

 function getUnique(arr, comp) { // Get a count of matching objects const counts = new Map(); for (const {[comp]: value} of arr) { const count = counts.get(value) || 0; // `get` returns `undefined` if it's // not there; we replace that with 0 counts.set(value, count + 1); } // Return only the unique ones return arr.filter(({[comp]: value}) => counts.get(value) === 1); } const rows = [ {type: "global", count: 6, name: "Name", orderliness: 1}, {type: "global", count: 5, name: "Name", orderliness: 2}, {type: "local", count: 1, name: "Name", orderliness: 3}, {type: "global", count: 8, name: "Name", orderliness: 3}, {type: "local", count: 2, name: "Name", orderliness: 1}, ]; // Get the unique rows, create new rows for the "other" // type with count = 0 and push them into `rows` rows.push(...getUnique(rows, 'orderliness').map(entry => ({...entry, type: entry.type === "global"? "local": "global", count: 0 }))); console.log(rows);