Explain the related methods of returning multiple specified columns in an array in PHP

array array_column ( array $input , mixed $column_key [, mixed $index_key = null ] )

<?php$arr = array(    array(&#39;id&#39;=>1001, &#39;name&#39;=>&#39;fdipzone&#39;, &#39;age&#39;=>18, &#39;profession&#39;=>&#39;programmer&#39;),    array(&#39;id&#39;=>1002, &#39;name&#39;=>&#39;terry&#39;, &#39;age&#39;=>19, &#39;profession&#39;=>&#39;designer&#39;),    array(&#39;id&#39;=>1003, &#39;name&#39;=>&#39;alex&#39;, &#39;age&#39;=>20, &#39;profession&#39;=>&#39;tester&#39;),
);$result = array_column($arr, &#39;name&#39;);

print_r($result);?>

Array(
    [0] => fdipzone
    [1] => terry
    [2] => alex
)

<?php/**
 * 返回数组中指定多列
 *
 * @param  Array  $input       需要取出数组列的多维数组
 * @param  String $column_keys 要取出的列名，逗号分隔，如不传则返回所有列
 * @param  String $index_key   作为返回数组的索引的列
 * @return Array
 */function array_columns($input, $column_keys=null, $index_key=null){
    $result = array();    $keys =isset($column_keys)? explode(&#39;,&#39;, $column_keys) : array();    if($input){        foreach($input as $k=>$v){            // 指定返回列
            if($keys){                $tmp = array();                foreach($keys as $key){                    $tmp[$key] = $v[$key];
                }
            }else{                $tmp = $v;
            }            // 指定索引列
            if(isset($index_key)){                $result[$v[$index_key]] = $tmp;
            }else{                $result[] = $tmp;
            }

        }
    }    return $result;
}// 演示代码$arr = array(    array(&#39;id&#39;=>1001, &#39;name&#39;=>&#39;fdipzone&#39;, &#39;age&#39;=>18, &#39;profession&#39;=>&#39;programmer&#39;),    array(&#39;id&#39;=>1002, &#39;name&#39;=>&#39;terry&#39;, &#39;age&#39;=>19, &#39;profession&#39;=>&#39;designer&#39;),    array(&#39;id&#39;=>1003, &#39;name&#39;=>&#39;alex&#39;, &#39;age&#39;=>20, &#39;profession&#39;=>&#39;tester&#39;),
);echo &#39;指定返回列及索引列&#39;.PHP_EOL;$result = array_columns($arr, &#39;name,profession&#39;, &#39;id&#39;);
print_r($result);echo PHP_EOL.&#39;指定返回列，不指定索引列&#39;.PHP_EOL;$result = array_columns($arr, &#39;name,profession&#39;);
print_r($result);echo PHP_EOL.&#39;不指定返回列，指定索引列&#39;.PHP_EOL;$result = array_columns($arr, null, &#39;id&#39;);
print_r($result);echo PHP_EOL.&#39;不指定返回列，不指定索引列&#39;.PHP_EOL;$result = array_columns($arr);
print_r($result);?>

指定返回列及索引列Array(
    [1001] => Array
        (
            [name] => fdipzone
            [profession] => programmer
        )

    [1002] => Array
        (
            [name] => terry
            [profession] => designer
        )

    [1003] => Array
        (
            [name] => alex
            [profession] => tester
        )

)

指定返回列，不指定索引列Array(
    [0] => Array
        (
            [name] => fdipzone
            [profession] => programmer
        )

    [1] => Array
        (
            [name] => terry
            [profession] => designer
        )

    [2] => Array
        (
            [name] => alex
            [profession] => tester
        )

)

不指定返回列，指定索引列Array(
    [1001] => Array
        (
            [id] => 1001
            [name] => fdipzone
            [age] => 18
            [profession] => programmer
        )

    [1002] => Array
        (
            [id] => 1002
            [name] => terry
            [age] => 19
            [profession] => designer
        )

    [1003] => Array
        (
            [id] => 1003
            [name] => alex
            [age] => 20
            [profession] => tester
        )

)

不指定返回列，不指定索引列Array(
    [0] => Array
        (
            [id] => 1001
            [name] => fdipzone
            [age] => 18
            [profession] => programmer
        )

    [1] => Array
        (
            [id] => 1002
            [name] => terry
            [age] => 19
            [profession] => designer
        )

    [2] => Array
        (
            [id] => 1003
            [name] => alex
            [age] => 20
            [profession] => tester
        )

)