JavaScript 中的多维数组

JavaScript 中不直接提供多维数组。如果我们想使用任何充当多维数组的东西，那么我们需要通过使用另一个一维数组来创建一个多维数组。所以 JavaScript 中的多维数组被称为另一个数组中的数组。我们需要将一些数组放入一个数组中，然后整个事情就像一个多维数组一样工作。其他数组将要插入的数组，该数组在我们的代码中用作多维数组。定义一个多维数组与定义一个普通的一维数组完全相同。

一维数组：

var arr = []; // Empty 1D array
var arr1 = ["A", "B", "C", "D"] // 1D array contains some alphabets
var arr1 = [1, 2, 3, 4, 5] // 1D array contains some digits

多维数组：

• 方法一：

  1st, need to define some 1D array
  var arr1 = ["ABC", 24, 18000];
  var arr2 = ["EFG", 30, 30000];
  var arr3 = ["IJK", 28, 41000];
  var arr4 = ["EFG", 31, 28000];
  var arr5 = ["EFG", 29, 35000];
  // "salary" defines like a 1D array but it already contains some 1D array
  var salary = [arr1, arr2, arr3, arr4, arr5]; 

  这里 arr1, arr2, ...arr5 是工资数组中的一些一维数组。

• 方法二：

  var salary = [
     ["ABC", 24, 18000],
     ["EFG", 30, 30000],
     ["IJK", 28, 41000],
     ["EFG", 31, 28000],
  ];

  在这里， salary数组就像一个多维数组。这种表示法称为数组字面量。

访问薪水数组的元素：

• 要访问数组元素，我们需要一个简单的基于索引的符号

  // This notation access the salary of "ABC" person which is 18000, 
  // [0] selects 1st row, and [2] selects the 3rd element
  // of that 1st row which is 18000
  salary[0][2];
  
  // Similarly, 
  salary[3][2]; // Selects 28000
  
  **This notation is used for both Method 1 and Method 2.
  

• 对于多次迭代，我们需要使用循环来访问元素，

  // This loop is for outer array
  for (var i = 0, l1 = salary.length; i < l1; i++) {
  
      // This loop is for inner-arrays
      for (var j = 0, l2 = salary[i].length; j < l2; j++) {
  
          // Accessing each elements of inner-array
          documents.write( salary[i][j] ); 
      }
  }

在多维数组中添加元素：在多维数组中添加元素可以通过内部数组或外部数组两种方式实现。内部数组可以通过两种不同的方式完成。

• 向内部数组添加元素：
  • 我们可以使用简单的方括号表示法在多维数组中添加元素。

    salary[3][3] = "India";
    
    // It adds "India" at the 4th index of 4th sub-array,
    // If we print the entire 4th sub-array, document.write(salary[3]);
    // the output will be :  ["EFG", 31, 28000, "India"]
    // indexing starts from 0

  • 我们可以使用push()方法在数组中添加元素。

    salary[3].push("India", "Mumbai");
    
    // It add "India" at the 4th index and "Mumbai" at
    // 5th index of 4th sub-array
    // If we print the entire 4th sub-array,
    // document.write(salary[3]);
    // The output will be :  ["EFG", 31, 28000, "India", "Mumbai"]
    // Indexing starts from 0

• 向外部数组添加元素：它与以前的方法非常相似。

  salary.push(["MNO", 29, 33300]);
  // This row added after the last row in the "salary" array

删除多维数组中的元素：我们可以使用pop()方法从内部数组中删除元素，也可以使用pop()方法删除整个内部数组。

// Remove last element from 4th sub-array
// That is 28000 indexing starts from 0
salary[3].pop(); 

// Removes last sub-array
// That is "["EFG", 31, 28000]"
salary.pop();

• 示例 1：

  // Prints a simple multidimensional array in JavaScript
  
  var arr1 = ["ABC", 24, 18000];
  var arr2 = ["EFG", 30, 30000];
  var arr3 = ["IJK", 28, 41000];
  var arr4 = ["EFG", 31, 28000];
  var arr5 = ["EFG", 29, 35000];
  var salary = [arr1, arr2, arr3, arr4, arr5]; 
  for(var i = 0; i < salary.length; i++) {
      document.write(salary[i] + "<br>");
  }

  输出：

  ABC, 24, 18000
  EFG, 30, 30000
  IJK, 28, 41000
  EFG, 31, 28000
  EFG, 29, 35000

• 示例 2：

  // Prints a simple multidimensional array in
  // JavaScript with different declaration
  
  var salary = [
     ["ABC", 24, 18000],
     ["EFG", 30, 30000],
     ["IJK", 28, 41000],
     ["EFG", 31, 28000],
  ]; 
  for(var i = 0; i < salary.length; i++) {
      document.write(salary[i] + "<br>");
  }
                      

  输出：

  ABC, 24, 18000
  EFG, 30, 30000
  IJK, 28, 41000
  EFG, 31, 28000
  EFG, 29, 35000

• 示例 3：

  // Prints a simple multidimensional array in JavaScript
  // where we just print the salary of a specific person
  
  var salary = [
     ["ABC", 24, 18000],
     ["EFG", 30, 30000],
     ["IJK", 28, 41000],
     ["EFG", 31, 28000],
  ]; 
  document.write("salary of 2nd person : " + salary[1][2] + "<br>");
  document.write("salary of 4th person : " + salary[3][2] + "<br>");
                      

  输出：

  salary of 2nd person : 30000
  salary of 4th person : 28000

• 示例 4：

  // Prints a simple multidimensional array in
  // JavaScript where we add elements in the array 
  // using simple square bracket and push() method
  
  var salary = [
     ["ABC", 24, 18000],
     ["EFG", 30, 30000],
     ["IJK", 28, 41000],
     ["EFG", 31, 28000],
  ]; 
    
  // Prints first array
  document.write("Original array :<br>");
  for(var i = 0; i < salary.length; i++) {
      document.write(salary[i] + "<br>");
  }
    
  // Adding "India" at the 4th index of 4th sub array
  salary[3][3] = "India";
    
  document.write("<br>after adding \"India\" at the 4th array :<br>");
  for(var i = 0; i < salary.length; i++) {
      document.write(salary[i] + "<br>");
  }
    
  document.write("<br>after adding \"USA\" and \"Canada\" "
       + "at the 3rd array using \"push()\" method :<br>");
  salary[2].push("USA", "Canada");
    
  // Adding "USA" and "Canada" in the 2nd sub-array
  for(var i = 0; i < salary.length; i++) {
      document.write(salary[i] + "<br>");
  }
   

  输出：

  Original array :
  ABC, 24, 18000
  EFG, 30, 30000
  IJK, 28, 41000
  EFG, 31, 28000
  
  after adding "India" at the 4th array :
  ABC, 24, 18000
  EFG, 30, 30000
  IJK, 28, 41000
  EFG, 31, 28000, India
  
  after adding "USA" and "Canada" at the 3rd array using "push()" method :
  ABC, 24, 18000
  EFG, 30, 30000
  IJK, 28, 41000, USA, Canada
  EFG, 31, 28000, India

• 示例 5：

  // Prints a simple multidimensional array in
  // JavaScript where we add a new inner array 
  
  var salary = [
     ["ABC", 24, 18000],
     ["EFG", 30, 30000],
     ["IJK", 28, 41000],
     ["EFG", 31, 28000],
  ]; 
    
  // Prints first array
  document.write("Original array :<br>");
    
  for(var i = 0; i < salary.length; i++) {
      document.write(salary[i] + "<br>");
  }
    
  document.write("<br>After adding a new inner array :<br>");
    
  // Pushing a new sub-array
  salary.push(["MNO", 29, 33300]);
    
  for(var i = 0; i < salary.length; i++) {
      document.write(salary[i] + "<br>");
  }
   

  输出：

  Original array :
  ABC, 24, 18000
  EFG, 30, 30000
  IJK, 28, 41000
  EFG, 31, 28000
  
  After adding a new inner array :
  ABC, 24, 18000
  EFG, 30, 30000
  IJK, 28, 41000
  EFG, 31, 28000
  MNO, 29, 33300

• 示例 6：

  // Prints a simple multidimensional array in
  // JavaScript where we remove a single element
  //and a entire sub-array
  
  var salary = [
     ["ABC", 24, 18000],
     ["EFG", 30, 30000],
     ["IJK", 28, 41000],
     ["EFG", 31, 28000],
  ]; 
    
  // Prints first array
  document.write("Original array :<br>");
    
  for(var i = 0; i < salary.length; i++) {
      document.write(salary[i] + "<br>");
  }
    
  document.write("<br>After removing last element " 
              + "of last inner array :<br>");
    
  // Removes the last element of 3rd sub-array
  salary[3].pop();
    
  for(var i = 0; i < salary.length; i++) {
      document.write(salary[i] + "<br>");
  }
    
  document.write("<br>After removing last inner array :<br>");
    
  // Removes last sub-array
  salary.pop();
    
  for(var i = 0; i < salary.length; i++) {
      document.write(salary[i] + "<br>");
  }
   

  输出：

  Original array :
  ABC, 24, 18000
  EFG, 30, 30000
  IJK, 28, 41000
  EFG, 31, 28000
  
  After removing last element of last inner array :
  ABC, 24, 18000
  EFG, 30, 30000
  IJK, 28, 41000
  EFG, 31
  
  After removing last inner array :
  ABC, 24, 18000
  EFG, 30, 30000
  IJK, 28, 41000

JavaScript 以网页开发而闻名，但它也用于各种非浏览器环境。您可以按照这个 JavaScript 教程和 JavaScript 示例从头开始学习 JavaScript。