PHP元素在元素之前和元素之后

I have a string and I change it into an array like this:

$a = "adik melempar kail ke tengah danau"

Array :

[0] => adik 
[1] => melempar
[2] => kail 
[3] => ke 
[4] => tengah 
[5] => danau

I have marked array[1] => melempar as verb (kata kerja).

How do I mark the next array (after array[1]) as object and the previous array (before array[1]) as subject?

An english example might be:

$a = "brother throw hook to the lake"

Array :

[0] => brother 
[1] => throw
[2] => hook
[3] => to 
[4] => the 
[5] => lake

Are you going to loop through the array looking for verbs? Assuming you have an array index variable $index, you could generally do something like this:

$words = explode(" ", $theSentence);
$index = 0;
foreach($words as $key=$theWord){
// apply your logic here that determines whether word is a verb
    if isVerb($theWord){
        $arrayResult[$index] = "verb";
        if($index > 0){
            $arrayResult[$index - 1 ] = 'subject';
            arrayResult[$index + 1 ] = 'object';
        }

    }
}


...

This is all very general, of course, since I don't know the context. You seem to have some logic in mind to determine what the words on either side of the verb are.