如何找到多维数组中最后出现的项的键？

Question

I need to find the key that corresponds to the last occurrence of (id = 100001203541047) in the following array:

[0] => Array
        (
            [id] => 10152583762905798_10152583800415798
            [from] => Array
                (
                    [id] => 100001203541047
                    [name] => Gangareddy Chealimealla
                )

            [message] => Desi Flipkart
            [created_time] => 2014-07-30T07:30:34+0000
            [like_count] => 0
            [user_likes] =>
            [can_comment] => 1
        )

    [1] => Array
        (
            [id] => 10152583762905798_10152583786375798
            [from] => Array
                (
                    [id] => 100001430479186
                    [name] => Pratik Das
                )

            [message] => flipkart rules! (y)
            [created_time] => 2014-07-30T07:16:56+0000
            [like_count] => 0
            [user_likes] =>
            [can_comment] => 1
        )

    [2] => Array
        (

            [id] => 10152583762905798_10152583802415798
            [from] => Array
                (
                    [id] => 100001203541047
                    [name] => Gangareddy Chealimealla
                )

            [message] => Desi Flipkart
            [created_time] => 2014-07-30T08:30:34+0000
            [like_count] => 0
            [user_likes] =>
            [can_comment] => 1
        )

I tried the following code, but it's returning 2 positions.

 foreach($arr as $key => $array)
 {
     if ( $array['from']['id'] === $id)
         echo $key."\n\n";
     }
 }

Why doesn't this only show the last one?

Answer 1

To do it simple, you could store them in an array and after the loop, take the last one.

change

echo $key."\n\n";

to

$ids[] = $key

And after the loop, you'll have your last occurence in

end($ids);

Hope it help you.

Answer 2

// function where you can pass the id you are looking for, eg.: 100001203541047.
function findElementById($id, $arr) {
    // iterate from the back, and you get the last match.
    for ($i = count($arr) - 1; $i >= 0; $i--) {
        $array = $arr[$i];
        if($array['from']['id'] === $id)){
            return $array; // if you find the element return it.
        }
    }
    return null; // return null if not found.
}

Example usage:

$elementYouAreLookingFor = findElementById(100001203541047, $arr);

Answer 3

Assuming the array is already sorted, you can use array_map to find the ones containing your search variable and then simply use array_pop to get the last result.

For example: this function only returns the last array value with the magic ID.

$magicID = '100001203541047';
function findSame($value){
    if($value['from']['id'] == $magicID){
        return $value;
    }
}

// $values should contain your data
$values = array(array(1,'from'=>array('id'=>'100001203541047'),3), array(1,'from'=>array('id'=>'20000'),4), array(2,'from'=>array('id'=>'100001203541047'),3));
$mapping = array_pop(array_filter(array_map('findSame', $values)));
var_dump($mapping);

Answer 4

Here's a fun one (PHP >= 5.5.0):

echo array_search($id,
     array_reverse(array_column(array_column($array, 'from'), 'id'), true));

Answer 5

The code you already wrote almost works. The problem is that it will just immediately print the key each time it encounters one that matches the id during the foreach loop.

foreach($arr as $key => $array) {
    if ( $array['from']['id'] === $id) {
        echo $key."\n\n";
    }
}

If instead you store the key in a variable, then after the loop is finished, the value in the variable will be the last one, and you can just print that.

$last = "";
foreach($arr as $key => $array) {
    if ( $array['from']['id'] === $id) {
        $last = $key;
    }
}
echo $last."\n\n";