Question

Let S be an associative array in PHP, I need to retrieve and extract from it the first element, both the value and the key.

I would use

value1=array_pop(S);

but it only gives me the value.

I can use

K=array_keys(S);
key1=array_pop(K);
value1=array_pop(S);

but it is complicated because it requires to have two copies of the same data. WHich is a confusing since the array is itself an element in an array of arrays. There must be a more elegant way to just read the couple key/value while extracting it.

Answer 1

// first
$value = reset($arr);
$key = key($arr);

(in that order)

See reset()^{PHP Manual},
key()^{PHP Manual}.

unset($arr[$key]); # in case you want to remove it.

However array_pop()^{PHP Manual} is working with the last element:

// last
$value = end($arr);
$key = key($arr);
unset($arr[$key]); # in case you want to remove it.

See end()^{PHP Manual}.

For the fun:

[$value, $key] = [reset($arr), key($arr)]; // first
[$value, $key] = [end($arr), key($arr)]; // last

(PHP 7.1+)

or

list($value, $key) = array(reset($arr), key($arr)); // first
list($value, $key) = array(end($arr), key($arr)); // last

(PHP 4.3+)

or

extract(array('value' => reset($arr), 'key' => key($arr))); // first
extract(array('value' => end($arr), 'key' => key($arr))); // last

(PHP 4.3+; Caution: extract() in use!)

or

// first
reset($arr);
list($key, $value) = each($arr);


// last
end($arr);
list($key, $value) = each($arr);

(Note: The each() function is deprecated since PHP 7.2.0 and gone since PHP 8.0.0)

or whatever style of play you like 😉

Dealing with empty arrays

It was missing so far to deal with empty arrays. So it’s a need to check if there is a last (first) element and if not, set the $key to null (as null can not be an array key):

// first
for ($key = null, $value = null; false !== $_ = reset($arr);)
{
    $value = $_;
    unset($arr[$key = key($arr)]);
    break;
}
unset($_);

// last
for ($key = null, $value = null; false !== $_ = end($arr);)
{
    $value = $_;
    unset($arr[$key = key($arr)]);
    break;
}
unset($_);

This will give for a filled array like $arr = array('first' => '1st', 'last' => '2nd.');:

string(4) "2nd." # value
string(4) "last" # key
array(1) { # leftover array
  ["first"]=>
  string(3) "1st"
}

And an empty array:

bool(false) # value
NULL # key
array(0) { # leftover array
}

Afraid of using unset?

In case you don’t trust unset() having the performance you need (of which I don’t think it’s really an issue, albeit I haven’t run any metrics), you can use the native array_pop() implementation as well (but I really think that unset() as a language construct might be even faster):

// first
reset($arr);
$key = key($arr);
$value = array_pop($arr);


// last
end($arr);
$key = key($arr);
$value = array_pop($arr);