数组部件访问

Question

我想更好地理解数组.请原谅我的基本问题,因为我刚刚在三周前打开了我的第一本php书.

我知道您可以使用foreach(或for循环)检索键/值对,如下所示.

 $stockprices= array("Google"=>"800", "Apple"=>"400", "Microsoft"=>"4",  "RIM"=>"15",  "Facebook"=>"30");

foreach ($stockprices as $key =>$price)

令我困惑的是像这样的多维数组:

$states=(array([0]=>array("capital"=> "Sacramento", "joined_union"=>1850, "population_rank"=> 1),
              [1]=>array("capital"=> "Austin", "joined_union"=>1845,"population_rank"=> 2),
              [2]=>array("capital"=> "Boston", "joined_union"=>1788,"population_rank"=> 14)
              ));

我的第一个问题非常基本:我知道"大写","joined_union","population_rank"是关键,"萨克拉门托","1850","1"是值(正确吗？).但你怎么称呼[0] [1] [2]？它们是"主键"和"大写"等子键吗？我找不到任何定义;无论是在书中还是在线.

主要问题是如何检索数组[0] [1] [2]？假设我想在1845年获得join_union的数组(或者在19世纪更加棘手),然后删除该数组.

最后,我可以将Arrays [0] [1] [2]命名为加利福尼亚州,德克萨斯州和马萨诸塞州吗？

$states=(array("California"=>array("capital"=> "Sacramento", "joined_union"=>1850, "population_rank"=> 1),
              "Texas"=>array("capital"=> "Austin", "joined_union"=>1845,"population_rank"=> 2),
              "Massachusetts"=>array("capital"=> "Boston", "joined_union"=>1788,"population_rank"=> 14)
              ));

Answer 1

与其他语言不同，PHP 中的数组可以使用数字或字符串键。你选。（这不是PHP的一个深受喜爱的特性，其他语言嗤之以鼻！）

$states = array(
    "California"    => array(
        "capital"         => "Sacramento",
        "joined_union"    => 1850,
        "population_rank" => 1
    ),
    "Texas"         => array(
        "capital"         => "Austin",
        "joined_union"    => 1845,
        "population_rank" => 2
    ),
    "Massachusetts" => array(
        "capital"         => "Boston",
        "joined_union"    => 1788,
        "population_rank" => 14
    )
);

至于查询你拥有的结构，有两种方法
1）循环

$joined1850_loop = array();
foreach( $states as $stateName => $stateData ) {
    if( $stateData['joined_union'] == 1850 ) {
        $joined1850_loop[$stateName] = $stateData;
    }
}
print_r( $joined1850_loop );
/*
Array
(
    [California] => Array
        (
            [capital] => Sacramento
            [joined_union] => 1850
            [population_rank] => 1
        )

)
*/

2）使用array_filter函数：

$joined1850 = array_filter(
    $states,
    function( $state ) {
        return $state['joined_union'] == 1850;
    }
);
print_r( $joined1850 );
/*
Array
(
    [California] => Array
        (
            [capital] => Sacramento
            [joined_union] => 1850
            [population_rank] => 1
        )

)
*/

-

$joined1800s = array_filter(
    $states,
    function ( $state ){
        return $state['joined_union'] >= 1800 && $state['joined_union'] < 1900;
    }
);
print_r( $joined1800s );
/*
Array
(
    [California] => Array
        (
            [capital] => Sacramento
            [joined_union] => 1850
            [population_rank] => 1
        )

    [Texas] => Array
        (
            [capital] => Austin
            [joined_union] => 1845
            [population_rank] => 2
        )

)
*/