减少数组到字符串，避免foreach

Question

I've an array to reduce to string, but I've to do MANY times so I would like to use some array PHP function (some combination of array_walk, array_reduce,...) but none fit my needs, but I belive there's a solution that I miss. The code have to be PHP5.6 compliant too.

$list =[
    'k1' => 'vA1 vA2 vA2',
    'k2' => 'vB1 vB2 vB2',
    'k3' => '',
    'k4' => 'vC1 vC2 vC2',
    'k5' => NULL,
    'k6' => 'vD1 vD2 vD2',
];

function reduce($list){
    $_buff="";
    $_sep="";
    foreach ($list as $k => $v){
        if($v===null){
            continue;
        }
        $_buff.="$_sep$k $v";
        $_sep="; ";
    }
    return $_buff;
}

echo reduce($list)."
";

The expected result is

k1 vA1 vA2 vA2; k2 vB1 vB2 vB2; k3 ; k4 vC1 vC2 vC2; k6 vD1 vD2 vD2

Please note the different behavior if value is an empty string or null.

Answer 1

I dont think there will be significant execution time difference with foreach or any array_* function. It will matter only if records increase more than 100K I guess.

$result = array();

array_walk($list, function($value, $key) use (&$result) {
    if($value!==null) {
        $result[] = $key .' '. $value;
    }
});

print_r(implode('; ', $result));

Why don't you compare the time taken from all answer and choose the best one ;)