数组降维-递归的归纳整理——数组降维的方法有三种半

1、朴素的转换

二维数组降维

这里有个容易出现的问题就是，必须要对元素进行是否是数组的判断，因为数组和字符串都有length属性，是数组的话，就是降维操作，是字符串的话，就会把字符串拆解了；还有就是数字没有length，所以数字元素的length的值是报错的，当前for循环无法执行，只有是数组或字符串才会有输出，所以必须要判断元素的属性

var arrs = ['3', 'we', 'w3', ['e', 'g'], 1, 2, 3, [4, 5]];

function jiangwei(arrs) {
  var newarrs = [];
  for (var i = 0; i < arrs.length; i++) {
    if (arrs[i] instanceof Array) {
      for (var j = 0; j < arrs[i].length; j++) {
        newarrs.push(arrs[i][j])
      }
    } else {
      newarrs.push(arrs[i])
    }
  }
  return newarrs
}
jiangwei(arrs);//["3", "we", "w3", "e", "g", 1, 2, 3, 4, 5]

多维数组降维

var arrs = [1, [23, 32], 42, [0, 33, [55, 39, [10, 331, [15, 34]]]]];

function jiangwei1(arrs) {
  var newarrs = [];
  function digui(arrs) {
    for (var i = 0; i < arrs.length; i++) {
      if (arrs[i] instanceof Array) {
        digui(arrs[i]);
      } else {
        newarrs.push(arrs[i]);
      }
    }
  }
  digui(arrs);
  return newarrs
}
jiangwei1(arrs);//[1, 23, 32, 42, 0, 33, 55, 39, 10, 331, 15, 34]

2、使用数组的concat方法

二维数据降维

var arrs = ['3', 'we', 'w3', ['e', 'g'], 1, 2, 3, [4, 5]];

function jiangwei2(arrs){
  var newarrs=[];
  for(var i=0;i<arrs.length;i++){
      newarrs=newarrs.concat(arrs[i])
  }
  return newarrs
}
jiangwei2(arrs);//["3", "we", "w3", "e", "g", 1, 2, 3, 4, 5]

多维数组降维

var arrs = [1, ['3', 'we',], 42, [0, 33, [55,  [10, 331, [15, 34]]]]];

function jiangwei3(arrs){
  var newarrs=[];
  function digui(arrs){
    for (var i=0;i<arrs.length;i++){
      if (arrs[i] instanceof Array){
          digui(arrs[i]);
      }else{
        newarrs=newarrs.concat(arrs[i]);
      }
    }
  }
  digui(arrs);
  return newarrs
}
jiangwei3(arrs);//[1, "3", "we", 42, 0, 33, 55, 10, 331, 15, 34]

3、利用apply和concat转换

二维数组降维

var arrs = ['3', 'we', 'w3', ['e', 'g'], 1, 2, 3, [4, 5]];

function jiangwei4(arrs){
  return Array.prototype.concat.apply([],arrs);
}
jiangwei4(arrs);//["3", "we", "w3", "e", "g", 1, 2, 3, 4, 5]

多维数组降维

var arrs = [1, ['3', 'we',], 42, [0, 33, [55, [10, 331, [15, 34]]]]];

function jiangwei5(arrs) {
  for (var i = 0; i < arrs.length; i++) {
    if (arrs[i] instanceof Array) {
      arrs[i] = jiangwei5(arrs[i]);
    }
  }
  return Array.prototype.concat.apply([], arrs);
}
jiangwei5(arrs);//[1, "3", "we", 42, 0, 33, 55, 10, 331, 15, 34]

4、toSthing方法

在研究降维的过程中，使用了数组的toSting方法，另一个角度看，也算是数组的降维了，当有局限性，全部是字符串的数组，是没有问题的，带有数字的数组，数字也会变成字符串，

而且其他类型也都会有所变化

String-String

Number-String

Boolean-String

Object-String-[object Object]

Function-String-函数表达式

Null-空白

Undefined-空白

var arrs = [1, ['3', 'we',], 42, [0, 33, [55, [10, 331, [15, 34]]]]];
arrs.toString();//"1,3,we,42,0,33,55,10,331,15,34"
arrs.toString().split(",");//["1", "3", "we", "42", "0", "33", "55", "10", "331", "15", "34"]

var arrs=[1,[2,'3'],[{'a':33},function(){alert(333)}],[4,[true,[null,[undefined]]]]];
arrs.toString();//"1,2,3,[object Object],function (){alert(333)},4,true,,"
arrs.toString().split(",");//["1", "2", "3", "[object Object]", "function (){alert(333)}", "4", "true", "", ""]