数组比较，用新数组覆盖老数组值

Question

//老数组{form_id: 1, field_id: 10, data: "215", member_id: 101}{form_id: 12, field_id: 2, data: "215212", member_id: 101}{form_id: 2, field_id: 31, data: "123", member_id: 101}//新数组{form_id: 2, field_id: 31, data: "123321", member_id: 101}需求：在老数组中找出form_id、field_id、member_id值与新数组对应值相同的数组，然后用新数组中data的值替换老数组的值。感谢～～

Answer 1

方法一，直接遍历搜寻

//老数组

const olds = [

    { form_id: 1, field_id: 10, data: "215", member_id: 101 },

    { form_id: 12, field_id: 2, data: "215212", member_id: 101 },

    { form_id: 2, field_id: 31, data: "123", member_id: 101 }

];

//新数组

const news = [

    { form_id: 2, field_id: 31, data: "123321", member_id: 101 }

];

function itemEquals(a, b) {

    return a.form_id === b.form_id

        && a.field_id === b.field_id

        && a.member_id === b.member_id

}

// 遍历旧数据，对每个元素去遍历新数组，查找是否有对应数据

olds.forEach(item => {

    const found = news.find(n => itemEquals(n, item));

    if (found) {

        item.data = found.data;

    }

});

console.log(olds);

上面的方面在新数据较大的时候，查询效率会比较低，那就可以采用拼接唯一ID的方法来处理

// 根据几个属性生成唯一键，注意间隔字符的选中，一定不能造成歧义

function unique(item) {

    return `${item.form_id}-${item.field_id}-${item.member_id}`;

}

const dict = news.reduce((dict, item) => {

    dict[unique(item)] = item;

    return dict;

}, {});

olds.forEach(item => {

    const found = dict[unique(item)];

    if (found) {

        item.data = found.data

    }

});

Answer 2

提供一个思路。如果数组元素比较少，可以穷举遍历，三层循环，复杂度较高。
如果数组元素比较多，可以考虑用空间换时间。将新数组转成容易查找的数据结构，比如多维数组，多层map，树，等，然后遍历老数组，一边遍历一边比较，找到一个就设置，找不到就跳过

Answer 3

let oldArray = [

  {form_id: 1, field_id: 10, data: "215", member_id: 101},

  {form_id: 12, field_id: 2, data: "215212", member_id: 101},

  {form_id: 2, field_id: 31, data: "123", member_id: 101}

];

let newArray = [{form_id: 2, field_id: 31, data: "123321", member_id: 101}];

for (let i = 0; i < oldArray.length; i++) {

  for (let a of newArray) {

    const o = oldArray[i];

    if (o.form_id === a.form_id && o.field_id === a.field_id && o.member_id === a.member_id) {

      oldArray[i].data = a.data;

    }

  }

}

console.log(oldArray);

输出：

[ { form_id: 1, field_id: 10, data: '215', member_id: 101 },

  { form_id: 12, field_id: 2, data: '215212', member_id: 101 },

  { form_id: 2, field_id: 31, data: '123321', member_id: 101 } ]