如何仅 flatten/reduce 最深或以其他方式指定的第 N 维数组级别

Question

假设一个N维数组，例如

const array = [
  "1",
  ["2","2"],
  [["3","3"],["3","3"]],
  [
    [
      [["4","4"],"3"],
      [["4","4"],"3"]
    ],
  ],
  [["3","3"],["3","3"]],
  ["2","2"],
  "1"
];

我只能找到从索引的浅端向上展平数组的方法，但我需要 flatten/reduce 或以其他方式仅处理最深（或任意）索引级别。

当运行最深层次时，我正在寻找一个数组输出类似

的东西

array = [
  "1",
  ["2","2"],
  [["3","3"],["3","3"]],
  [
    [
      ["4,4","3"],
      ["4,4","3"]
    ],
  ],
  [["3","3"],["3","3"]],
  ["2","2"],
  "1"
];

我找不到不是垃圾的解决方案...（over-complicated/incredibly 乱七八糟）任何帮助将不胜感激

Answer 1

您可以使用递归函数获取数组和所需级别，然后在级别为 1 时停止重复出现，此时您只需过滤掉该（子）数组中的非数组值：

function extractLevel(arr, level) {
    return level <= 1 
        ? arr.filter(val => !Array.isArray(val))
        : arr.filter(Array.isArray)
             .flatMap(arr => extractLevel(arr, level-1));
}

// demo
const array = ["1",["2","2"],[["3","3"],["3","3"]],[[[["4","4"],"3"],[["4","4"],"3"]],[["",""],["",""]]],[["3","3"],["3","3"]],["2","2"],"1"];
// extract the values (not arrays) at level 3:
console.log(extractLevel(array, 3));

Answer 2

您可以创建一个函数来获取您想要展平的数据和级别，并且只会展平该级别。然后要获得最后一个级别，您可以创建另一个函数。

const array = ["1",["2","2"],[["3","3"],["3","3"]],[[[["4","4"],"3"],[["4","4"],"3"]],[["",""],["",""]]],[["3","3"],["3","3"]],["2","2"],"1"];

function lastLvl(data, lvl = 0) {
  return data.reduce((r, e) => {
    if (lvl > r) r = lvl

    if (Array.isArray(e)) {
      const nlvl = lastLvl(e, lvl + 1);
      if (nlvl > r) r = nlvl
    }

    return r
  }, 0)
}

function flattenLvl(data, lvl, clvl = 1) {
  return data.reduce((r, e) => {
    if (Array.isArray(e)) {
      const nested = flattenLvl(e, lvl, clvl + 1);
      if (clvl == lvl) r.push(...nested);
      else r.push(nested)
    } else {
      r.push(e)
    }

    return r;
  }, [])
}

const lvl = lastLvl(array)
const result = flattenLvl(array, lvl)
console.log(result)

如何仅 flatten/reduce 最深或以其他方式指定的第 N 维数组级别

How to flatten/reduce only the deepest or otherwise specicified level of an Nth-dimensional array

javascript

arrays

flatten

multidimensional-array