用javascript实现数组交叉的最简单、无库代码是什么?我想写

intersection([1,2,3], [2,3,4,5])

并获得

[2, 3]

当前回答

对于只包含字符串或数字的数组,你可以做一些排序,就像其他答案一样。对于任意对象数组的一般情况,我不认为你可以避免这样做。下面将为您提供任意数量的数组的交集作为arrayIntersection的参数:

var arrayContains = Array.prototype.indexOf ?
    function(arr, val) {
        return arr.indexOf(val) > -1;
    } :
    function(arr, val) {
        var i = arr.length;
        while (i--) {
            if (arr[i] === val) {
                return true;
            }
        }
        return false;
    };

function arrayIntersection() {
    var val, arrayCount, firstArray, i, j, intersection = [], missing;
    var arrays = Array.prototype.slice.call(arguments); // Convert arguments into a real array

    // Search for common values
    firstArray = arrays.pop();
    if (firstArray) {
        j = firstArray.length;
        arrayCount = arrays.length;
        while (j--) {
            val = firstArray[j];
            missing = false;

            // Check val is present in each remaining array 
            i = arrayCount;
            while (!missing && i--) {
                if ( !arrayContains(arrays[i], val) ) {
                    missing = true;
                }
            }
            if (!missing) {
                intersection.push(val);
            }
        }
    }
    return intersection;
}

arrayIntersection( [1, 2, 3, "a"], [1, "a", 2], ["a", 1] ); // Gives [1, "a"]; 

其他回答

如果只使用关联数组呢?

function intersect(a, b) {
    var d1 = {};
    var d2 = {};
    var results = [];
    for (var i = 0; i < a.length; i++) {
        d1[a[i]] = true;
    }
    for (var j = 0; j < b.length; j++) {
        d2[b[j]] = true;
    }
    for (var k in d1) {
        if (d2[k]) 
            results.push(k);
    }
    return results;
}

编辑:

// new version
function intersect(a, b) {
    var d = {};
    var results = [];
    for (var i = 0; i < b.length; i++) {
        d[b[i]] = true;
    }
    for (var j = 0; j < a.length; j++) {
        if (d[a[j]]) 
            results.push(a[j]);
    }
    return results;
}

使用Array.prototype.filter和Array.prototype.includes的组合:

const filteredArray = array1.filter(value => array2.includes(value));

对于较旧的浏览器,使用Array.prototype.indexOf且不使用箭头函数:

var filteredArray = array1.filter(function(n) {
    return array2.indexOf(n) !== -1;
});

NB !.includes和. indexof都在内部使用===来比较数组中的元素,所以如果数组包含对象,它只比较对象引用(而不是对象的内容)。如果你想指定自己的比较逻辑,请使用Array.prototype.some。

使用jQuery:

var a = [1,2,3];
var b = [2,3,4,5];
var c = $(b).not($(b).not(a));
alert(c);

我认为在内部使用一个对象可以帮助计算,也可以提高性能。

//方法维护每个元素的计数,也适用于负元素

function intersect(a,b){
    
    const A = {};
    a.forEach((v)=>{A[v] ? ++A[v] : A[v] = 1});
    const B = {};
    b.forEach((v)=>{B[v] ? ++B[v] : B[v] = 1});
    const C = {};
    Object.entries(A).map((x)=>C[x[0]] = Math.min(x[1],B[x[0]]))
    return Object.entries(C).map((x)=>Array(x[1]).fill(Number(x[0]))).flat();
}
const x = [1,1,-1,-1,0,0,2,2];
const y = [2,0,1,1,1,1,0,-1,-1,-1];
const result = intersect(x,y);
console.log(result);  // (7) [0, 0, 1, 1, 2, -1, -1]

这是一个现代和简单的ES6方式来做,也非常灵活。 它允许您指定多个数组作为与主题数组进行比较的数组,并且可以在包含和独占模式下工作。

// =======================================
// The function
// =======================================

function assoc(subjectArray, otherArrays, { mustBeInAll = true } = {}) {
  return subjectArray.filter((subjectItem) => {
    if (mustBeInAll) {
      return otherArrays.every((otherArray) =>
        otherArray.includes(subjectItem)
      );
    } else {
      return otherArrays.some((otherArray) => otherArray.includes(subjectItem));
    }
  });
}

// =======================================
// The usage
// =======================================

const cheeseList = ["stilton", "edam", "cheddar", "brie"];
const foodListCollection = [
  ["cakes", "ham", "stilton"],
  ["juice", "wine", "brie", "bread", "stilton"]
];

// Output will be: ['stilton', 'brie']
const inclusive = assoc(cheeseList, foodListCollection, { mustBeInAll: false }),

// Output will be: ['stilton']
const exclusive = assoc(cheeseList, foodListCollection, { mustBeInAll: true })

实例:https://codesandbox.io/s/zealous-butterfly-h7dgf?fontsize=14&hidenavigation=1&theme=dark