获取二维数组中指定字段的值，并且将值组成一维数组

从数据库获取多个数据时往往是二维数组，但是有时候我们需要获取数组里面的某一键的数据。有两种方法：foreach()循环和Array()函数

示例数组，获取二维数组里面的device_token的值并且放在一维数组里面：

$arr = array(
    0 => array(
        'device_token' => 'AnBWyVMD1u0qKkNrD44h8BaFjROX5qCRgDjEG6CCFtFd',
        'shebei' => 'android'
    ),
    1 => array(
        'device_token' => 'Ap0pTms6pvxMtsvrqCvzbqknLkO6KEIJnk3x9iGYlgd8',
        'shebei' => 'android'
    ),
    2 => array(
        'device_token' => '6aa7d1356e75a56758a0fdc40b776d0cab7fa8889de546106888d3b3c5eee872',
        'shebei' => 'ios'
    ),
    3 => array(
        'device_token' => '9e9854b6b6f02c58aa8838619b25e18139558dca9f69e2abbc6f9b88630ff269',
        'shebei' => 'ios'
    ),
    4 => array(
        'device_token' => 'ApKqVYFWWXNds9CnveE24ysTZ942nw5P2o5lE6KJegqg',
        'shebei' => 'android'
    ),
    5 => array(
        'device_token' => '',
        'shebei' => 'ios'
    ),
　　6 => array(
　　　　'device_token' => 0,
　　　　'shebei' => 'android'
　　)
);

一、foreach()循环

$IOS_token = array();
$android_token = array();
if(!empty($arr) && count($res) != 0){
    foreach($arr as $key => $val){
        if($val['shebei'] == 'android'){
            $android_token[] = $val['device_token'];
        }elseif($val['shebei'] == 'ios'){
            $IOS_token[] = $val['device_token'];
        }
    }
}

二、Array()函数

$ios_res = array_column(array_filter($arr,function($val){
    if($val['shebei'] == 'ios'){
        return $val['device_token'];
    }else{
        return false;
    }
}),'device_token');
$android_res = array_column(array_filter($arr,function($value){
    if($value['shebei'] == 'android'){
        return $value['device_token'];
    }else{
        return false;
    }
}),'device_token');

返回结果一维数组：

Array
(
    [ios] => Array
        (
            [0] => 6aa7d1356e75a56758a0fdc40b776d0cab7fa8889de546106888d3b3c5eee872
            [1] => 9e9854b6b6f02c58aa8838619b25e18139558dca9f69e2abbc6f9b88630ff269
        )

    [android] => Array
        (
            [0] => AnBWyVMD1u0qKkNrD44h8BaFjROX5qCRgDjEG6CCFtFd
            [1] => Ap0pTms6pvxMtsvrqCvzbqknLkO6KEIJnk3x9iGYlgd8
            [2] => ApKqVYFWWXNds9CnveE24ysTZ942nw5P2o5lE6KJegqg
        )

)

原始数组$arr中ios其实有三个，但是有一个是空值，所以array_filter()函数给过滤掉了；android分类下的0也被过滤掉了。

注意点：array_filter会过滤掉任何等于FALSE的值，也就是说  0值，空字符串，null，都会被过滤