如何基于二维数组中子数组的第二个值统计各年份水果数量？

Python 实现 #

基础字典遍历法 #

data = [['apples', 2020], ['pears', 2020], ['apples', 2021], ['melons', 2020], ['peaches', 2021], ['pears', 2019]]
year_count = {}
for _, year in data:
    # 若年份已存在则加1，不存在则初始化为1
    year_count[year] = year_count.get(year, 0) + 1
print(year_count)
# 输出: {2020: 3, 2021: 2, 2019: 1}

使用collections.defaultdict简化代码 #

from collections import defaultdict

data = [['apples', 2020], ['pears', 2020], ['apples', 2021], ['melons', 2020], ['peaches', 2021], ['pears', 2019]]
year_count = defaultdict(int)
for _, year in data:
    year_count[year] += 1
# 转换为普通字典输出
print(dict(year_count))
# 输出: {2020: 3, 2021: 2, 2019: 1}

JavaScript 实现 #

遍历统计 #

const data = [['apples', 2020], ['pears', 2020], ['apples', 2021], ['melons', 2020], ['peaches', 2021], ['pears', 2019]];
const yearCount = {};
data.forEach(([_, year]) => {
    yearCount[year] = (yearCount[year] || 0) + 1;
});
console.log(yearCount);
// 输出: {2019: 1, 2020: 3, 2021: 2}

使用reduce方法 #

const data = [['apples', 2020], ['pears', 2020], ['apples', 2021], ['melons', 2020], ['peaches', 2021], ['pears', 2019]];
const yearCount = data.reduce((acc, [_, year]) => {
    acc[year] = (acc[year] || 0) + 1;
    return acc;
}, {});
console.log(yearCount);
// 输出: {2019: 1, 2020: 3, 2021: 2}

内容的提问来源于stack exchange，提问作者unnamed_road