56 lines
1.3 KiB
JavaScript
56 lines
1.3 KiB
JavaScript
// arr.reduce(
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// callback(accumulator, currentValue[, currentIndex[, array]])
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// [, initialValue]
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// )
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const data1 = [1, 2, 3, 4, 5];
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// 没有使用初始值，则 sum 被初始为 1，cur从2开始, ..., ...
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let rst1 = data1.reduce((sum, cur) => {
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return sum += cur
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})
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console.log(rst1)
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const data2 = [1, 2, 3, 4, 5];
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// 为初始值【1】，则temp被初始为【1】，cur从1开始, ..., ...
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let rst2 = data2.reduce((temp, cur) => {
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return temp *= cur
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}, 1)
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console.log(rst2);
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const fruits = ['apple', 'banana', 'apple', 'banana', 'apple'];
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const rst3 = fruits.reduce((acc, cur) => {
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if (!acc[cur])
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acc[cur] = 1;
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else
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acc[cur]++;
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return acc;
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}, {});
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console.log(rst3);
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const people = [
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{ name: 'zs', age: 25 },
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{ name: 'ls', age: 30 },
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{ name: 'ww', age: 25 },
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{ name: 'sb', age: 30 }
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];
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// 按年龄进行汇总，acc初始为{}，cur从zs这条数据开始
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const rst4 = people.reduce((acc, cur) => {
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const age = cur.age;
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if (!acc[age])
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acc[age] = [];
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acc[age].push(cur);
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return acc;
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}, {});
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console.log(rst4);
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/*
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# node reduce.js
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15
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120
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{ apple: 3, banana: 2 }
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{
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'25': [ { name: 'zs', age: 25 }, { name: 'ww', age: 25 } ],
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'30': [ { name: 'ls', age: 30 }, { name: 'sb', age: 30 } ]
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}
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*/
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