生成数组值列表时奇怪的PHP行为

问题描述：

I have a multidimensional PHP array of the following form:

Array
(
    [0] => Array
        (
            [id] => 45
            [date] => 2013-05-16
        )

    [1] => Array
        (
            [id] => 30
            [date] => 2013-12-10
        )

    [2] => Array
        (
            [id] => 26
            [date] => 2014-03-27
        )

    [3] => Array
        (
            [id] => 34
            [date] => 2014-03-27
        )

)

I am trying to generate a list of the [id] values, separated by commas, using the following PHP code:

foreach ($my_array as $key => $value) { 
    if ($key == 0) {
        $id_list = $value[id];
    }
    if ($key !== 0 ) {
        $id_list .= "," . $value[id];
    }
}

I was hoping this would return

45,30,26,34

...but for some reason it returns

45,30,26,26

i.e. the penultimate ID is duplicated and the final ID is missed off. I have been staring at this for a while now but I can't see where I'm going wrong. Have I missed something obvious?

我有一个以下形式的多维PHP数组： p>

 数组
（
 [0] =＆gt;数组
（
 [id] =＆gt; 45 
 [日期] =＆gt; 2013-05-16 
）
 
 [1] =  ＆gt;数组
（
 [id] =＆gt; 30 
 [日期] =＆gt; 2013-12-10 
）
 
 [2] =＆gt;数组
（
 [id]  =＆gt; 26 
 [date] =＆gt; 2014-03-27 
）
 
 [3] =＆gt;数组
（
 [id] =＆gt; 34 
 [date] =＆gt;  ; 2014-03-27 
）
 
）
  code>  pre> 
 
 我正在尝试生成[id]值列表，以逗号分隔，使用 以下PHP代码： p> 
 
 
  foreach（$ my_array as $ key =＆gt; $ value）{
 if（$ key == 0）{
 $ id_list = $  value [id]; 
} 
 if（$ key！== 0）{
 $ id_list。=“，”。  $ value [id]; 
} 
} 
  code>  pre> 
 
 我希望这会返回 p> 
 
 
  45  ，30,26,34 
  code>  pre> 
 
  ...但由于某种原因它会返回 p> 
 
 
  45,30，  26,26 
 代码>  PRE> 
 
 即 倒数第二个ID重复，最终ID丢失。 我一直在盯着这一段时间，但我看不出我哪里出错了。 我错过了一些明显的东西吗？ p> 
  div>

答

The better solution would be to not use those if() at all:

$ids = array();
foreach($arr as $val) {
   $ids[] = $val['id'];
}

$id_str = implode(',', $ids);

生成数组值列表时奇怪的PHP行为

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