Php 简明教程

PHP - Multidimensional Array

多维数组是数组的数组。在 PHP 数组中，每个元素可以是另一个数组。如果数组由值或键值对组成，且值属于标量的单数类型，则它是一维数组。如果数组中的每个元素都是一个或多个标量值组成的数组，则它是二维数组。

PHP 数组也可能是一个二维关联数组，其中外层数组的每个元素都是键值对，而该值又是另一个关联数组。

# one dimensional indexed array
$arr = [10, 20, 30, 40];

# one dimensional associative array
$arr = ["key1"=> "val1", "key2" => "val2", "key3" => "val3"];

# two dimensional indexed array
$arr = [
   [1,2,3,4],
   [10, 20, 30, 40],
   [100, 200, 300, 400]
];

# two dimensional associative array
$arr = [
   "row1" => ["key11" => "val11", "key12" => "val12", "key13" => "val13"],
   "row2" => ["key21" => "val21", "key22" => "val22", "key23" => "val23"],
   "row3" => ["key31" => "val31", "key32" => "val32", "key33" => "val33"]
];

Iterating over a 2D Array

遍历二维数组中的所有元素需要两个嵌套的循环。 foreach 循环更适合数组遍历。二维数组类似于行和列中数据的表格形式表示。

Example

以下示例展示了如何以表格形式重现二维数组 −

<?php
   $tbl = [
      [1,2,3,4],
      [10, 20, 30, 40],
      [100, 200, 300, 400]
   ];
   echo ("\n");
   foreach ($tbl as $row){
      foreach ($row as $elem){
         $val = sprintf("%5d", $elem);
         echo $val;
      }
      echo "\n";
   }
?>

它将生成以下 output −

  1    2    3    4
 10   20   30   40
100  200  300  400

Example

我们也可以用两个嵌套的 foreach 循环来遍历二维关联数组。在 row-key 和 row-value 变量中解包外层数组的每一行，并用内层 foreach 循环遍历每一行元素。

<?php
   $tbl = [
      "row1" => ["key11" => "val11", "key12" => "val12", "key13" => "val13"],
      "row2" => ["key21" => "val21", "key22" => "val22", "key23" => "val23"],
      "row3" => ["key31" => "val31", "key32" => "val32", "key33" => "val33"]
   ];

   echo ("\n");
   foreach ($tbl as $rk=>$rv){
      echo "$rk\n";
      foreach ($rv as $k=>$v){
         echo "$k => $v  ";
      }
      echo "\n";
   }
?>

它将生成以下 output −

row1
key11 => val11  key12 => val12  key13 => val13
row2
key21 => val21  key22 => val22  key23 => val23
row3
key31 => val31  key32 => val32  key33 => val33

Accessing the Elements in a 2D Array

访问和修改数组中元素的 $arr[$key] 语法也可以扩展到二维数组。对于二维索引数组，可以使用表达式 “@ {s7}” 获取和分配第 i 行的第 j 个元素。

Example

<?php
   $tbl = [[1,2,3,4], [10, 20, 30, 40], [100, 200, 300, 400]];

   # prints number in index 2 of the row 2
   print ("Value at [2], [2] :" . $tbl[2][2]);
?>

它将生成以下 output −

Value at [2], [2] :300

类似地，可以将第 i 行和第 j 列的值设置为另一个值。

$tbl[2][2] = 250;

Example

如果它是一个二维关联数组，我们需要使用所需列的行键和键值变量来访问或修改其值。

<?php
   $tbl = [
   "row1" => ["key11" => "val11", "key12" => "val12", "key13" => "val13"],
   "row2" => ["key21" => "val21", "key22" => "val22", "key23" => "val23"],
   "row3" => ["key31" => "val31", "key32" => "val32", "key33" => "val33"]
   ];

   print "value at row2 - key22 is " . $tbl["row2"]["key22"];
?>

它将生成以下 output −

value at row2 - key22 is val22

Multi-dimensional Array

在上面的示例中，我们有了一个数组，其中每个键的关联值是另一组键值对集合，我们称之为二维数组。该概念可以扩展到任意多个级别。例如，如果内层数组中的每个元素将其键与另一个数组关联，则它将变成一个三维数组。

以下是 example 三维数组的示例 −

$arr3D = [
   [
      [1, 0, 9],
      [0, 5, 6],
      [1, 0, 3]
   ],
   [
      [0, 4, 6],
      [0, 0, 1],
      [1, 2, 7]
   ],
];

Example

要遍历这样的三维数组，我们需要三个嵌套的 foreach 循环，如下所示 −

<?php
   $arr3D = [
      [[1, 0, 9],[0, 5, 6],[1, 0, 3]],
      [[0, 4, 6],[0, 0, 1],[1, 2, 7]],
   ];

   foreach ($arr3D as $arr) {
      foreach ($arr as $row) {
         foreach ($row as $element) {
            echo "$element ";
         }
         echo "\n";
      }
      echo "\n";
   }
?>

它将生成以下 output −

1 0 9
0 5 6
1 0 3

0 4 6
0 0 1
1 2 7

然而，完全有可能声明一个扩展到任意维度的数组。为此，我们需要一个通用的解决方案来遍历任意维度的数组。

Recurve Traversal of Multidimensional Array

以下代码展示了一个递归函数，如果某个键的值是另一个数组，它会自己调用自己。如果我们向此函数传递任何数组作为参数，它将被遍历，显示其中的所有 k-v 对。

function showarray($arr) {
   foreach ($arr as $k=>$v) {
      if (is_array($v)) {
         showarray($v);
      } else {
         echo "$k => $v  ";
      }
   }
   echo "\n";
}

Example

让我们将上面的三维数组 $arr3D 传递给它并查看结果 −

<?php
   $arr3D = [
      [[1, 0, 9],[0, 5, 6],[1, 0, 3]],
      [[0, 4, 6],[0, 0, 1],[1, 2, 7]],
   ];

   function showarray($arr){
      foreach ($arr as $k=>$v){
         if (is_array($v)){
            showarray($v);
         } else {
            echo "$k => $v  ";
         }
      }
      echo "\n";
   }
   showarray($arr3D);
?>

它将生成以下 output −

0 => 1  1 => 0  2 => 9
0 => 0  1 => 5  2 => 6
0 => 1  1 => 0  2 => 3
0 => 0  1 => 4  2 => 6
0 => 0  1 => 0  2 => 1
0 => 1  1 => 2  2 => 7

此递归函数可用于任何类型的数组，无论是索引数组还是关联数组，还可以用于任何维度。

Example

让我们使用一个二维关联数组作为参数来展示 showarray() 函数 −

<?php
   $tbl = [
      "row1" => ["key11" => "val11", "key12" => "val12", "key13" => "val13"],
      "row2" => ["key21" => "val21", "key22" => "val22", "key23" => "val23"],
      "row3" => ["key31" => "val31", "key32" => "val32", "key33" => "val33"]
   ];

   function showarray($arr){
      foreach ($arr as $k=>$v){
         if (is_array($v)){
            showarray($v);
         } else {
            echo "$k => $v  ";
         }
      }
      echo "\n";
   }
   showarray($tbl);
?>

它将生成以下 output −

key11 => val11  key12 => val12  key13 => val13
key21 => val21  key22 => val22  key23 => val23
key31 => val31  key32 => val32  key33 => val33