使用PHP检索多维数组中的第一个键

Question

I would like to retrieve the first key from this multi-dimensional array.

Array
(
    [User] => Array
        (
            [id] => 2
            [firstname] => first
            [lastname] => last
            [phone] => 123-1456
            [email] => 
            [website] => 
            [group_id] => 1
            [company_id] => 1
        )

)

This array is stored in $this->data.

Right now I am using key($this->data) which retrieves 'User' as it should but this doesn't feel like the correct way to reach the result.

Are there any other ways to retrieve this result?

Thanks

Answer 1

There are other ways of doing it but nothing as quick and as short as using key() . Every other usage is for getting all keys. For example, all of these will return the first key in an array:

$keys=array_keys($this->data);
echo $keys[0]; //prints first key

foreach ($this->data as $key => $value)
{
    echo $key;
    break;
}

As you can see both are sloppy.

If you want a oneliner, but you want to protect yourself from accidentally getting the wrong key if the iterator is not on the first element, try this:

reset($this->data);

reset():

reset() rewinds array 's internal pointer to the first element and returns the value of the first array element.

But what you're doing looks fine to me. There is a function that does exactly what you want in one line; what else could you want?

Answer 2

使用此（PHP 5.5+）：

echo reset(array_column($this->data, 'id'));

Answer 3

I had a similar problem to solve and was pleased to find this post. However, the solutions provided only works for 2 levels and do not work for a multi-dimensional array with any number of levels. I needed a solution that could work for an array with any dimension and could find the first keys of each level.

After a bit of work I found a solution that may be useful to someone else and therefore I included my solution as part of this post.

Here is a sample start array:

    $myArray = array(
    'referrer' => array(
        'week' => array(
            '201901' => array(
                'Internal' => array(
                    'page' => array(
                        'number' => 201,
                        'visits' => 5
                    )
                ),
                'External' => array(
                    'page' => array(
                        'number' => 121,
                        'visits' => 1
                    )
                ),
            ),
            '201902' => array(
                'Social' => array(
                    'page' => array(
                        'number' => 921,
                        'visits' => 100
                    )
                ),
                'External' => array(
                    'page' => array(
                        'number' => 88,
                        'visits' => 4
                    )
                ),
            )
        )
    )
);

As this function needs to display all the fist keys whatever the dimension of the array, this suggested a recursive function and my function looks like this:

function getFirstKeys($arr){
    $keys = '';
    reset($arr);
    $key = key($arr);
    $arr1 = $arr[$key];
    if (is_array($arr1)){
        $keys .= $key . '|'. getFirstKeys($arr1);
    } else {
        $keys = $key;
    }
    return $keys;
}

When the function is called using the code:

$xx = getFirstKeys($myArray);
echo '<h4>Get First Keys</h4>';
echo '<li>The keys are: '.$xx.'</li>';

the output is:

Get First Keys

• The keys are: referrer|week|201901|Internal|page|number

I hope this saves someone a bit of time should they encounter a similar problem.