MongoDB中将嵌套数组合并为一维数组的实现方法

针对你提供的嵌套数组结构，以下是几种主流编程语言的实现方式，可将每个对象中的immunizationDetails二维数组转换为一维数组：

JavaScript 实现 #

利用数组原生的flat()方法快速扁平化数组，搭配map()遍历原数组即可完成转换：

const originalData = [
  {
    "immunizationDetails": [
      ["Rubella"],
      ["PCV13", "Tdap"]
    ]
  },
  {
    "immunizationDetails": [
      ["Hepatitis B", "HIB"],
      ["PCV13"]
    ]
  }
];

const transformedData = originalData.map(item => ({
  ...item,
  immunizationDetails: item.immunizationDetails.flat()
}));

console.log(transformedData);

flat()默认扁平化一层嵌套，刚好匹配你的需求；若存在更深层级嵌套，可传入参数（如flat(Infinity)）处理任意深度的嵌套数组。

Python 实现 #

可通过列表推导式或itertools.chain实现数组扁平化：

方式一：列表推导式 #

original_data = [
    {
        "immunizationDetails": [
            ["Rubella"],
            ["PCV13", "Tdap"]
        ]
    },
    {
        "immunizationDetails": [
            ["Hepatitis B", "HIB"],
            ["PCV13"]
        ]
    }
]

transformed_data = [
    {
        **item,
        "immunizationDetails": [vaccine for sublist in item["immunizationDetails"] for vaccine in sublist]
    }
    for item in original_data
]

print(transformed_data)

方式二：使用itertools.chain #

import itertools

original_data = [
    {
        "immunizationDetails": [
            ["Rubella"],
            ["PCV13", "Tdap"]
        ]
    },
    {
        "immunizationDetails": [
            ["Hepatitis B", "HIB"],
            ["PCV13"]
        ]
    }
]

transformed_data = [
    {
        **item,
        "immunizationDetails": list(itertools.chain.from_iterable(item["immunizationDetails"]))
    }
    for item in original_data
]

print(transformed_data)

两种方式均可将二维数组展开为一维，itertools.chain在处理大规模数据时性能更优。

内容的提问来源于stack exchange，提问作者Code The World