Split the strings of a flat array to create an array of associative rows

Try this, check the live demo

foreach($pks as $k => $v) {
    $values = explode('||', $v);
    $result[] = array_combine(range(1, count($values)), $values);

    //added
    $res[] = array_combine(['date', 'vessel'], $values) ;

}

result

Array
(
    [0] => Array
        (
            [1] => 2017-04-15
            [2] => KMTC_HOCHIMINH
        )

    [1] => Array
        (
            [1] => 2017-04-15
            [2] => OOCL_NAGOYA
        )

)

You can use array_walk() (or just foreach if you want):

array_walk($pks, function(&$a) {
    $a = array_combine(['date', 'vessel'], explode('||', $a));
});

Foreach method:

foreach($pks as $k => $v) {
    $pks[$k] = array_combine(['date', 'vessel'], explode('||', $v));
}

However, the key of each array won't be record, since it's impossible to have the same key multiple times.

Output:

Array
(
    [0] => Array
        (
            [date] => 2017-04-15
            [vessel] => KMTC_HOCHIMINH
        )

    [1] => Array
        (
            [date] => 2017-04-15
            [vessel] => OOCL_NAGOYA
        )

)

Bonus method because I like messing with arrays:

$pks = array_map('explode', array_fill(0, count($pks), '||'), $pks);

Some more solutions which provide the same, desired result. Demo

$arr = [
    '2017-04-15||KMTC_HOCHIMINH',
    '2017-04-15||OOCL_NAGOYA',
];

Make iterated get_defined_vars().

var_export(
    array_map(
        fn($v) => (fn($date, $vessel) => get_defined_vars())(...explode('||', $v)),
        $arr
    )
);

Make iterated array_combine() calls.

var_export(
    array_map(
        fn($v) => array_combine(['date', 'vessel'], explode('||', $v)),
        $arr
    )
);

Push reference variables into the result.

$result = [];
foreach ($arr as $v) {
    $result[] =& $row;
    [$row['date'], $row['vessel']] = explode('||', $v);
}
var_export($result);

Modify by reference using an Immediately Invoked Functional Expression.

foreach ($arr as &$v) {
    $v = (fn($date, $vessel) => get_defined_vars())(...explode('||', $v));
}
var_export($arr);