php: how to get associative array key from numeric index?

If I have:

$array = array( 'one' =>'value', 'two' => 'value2' );

how do I get the string one back from $array[1] ?

You don't. Your array doesn't have a key [1]. You could:

• Make a new array, which contains the keys:

   $newArray = array_keys($array);
   echo $newArray[0];
  

  But the value "one" is at $newArray[0], not [1].
  A shortcut would be:

   echo current(array_keys($array));
  

• Get the first key of the array:

    reset($array);
    echo key($array);
  

• Get the key corresponding to the value "value":

   echo array_search('value', $array);
  

This all depends on what it is exactly you want to do. The fact is, [1] doesn't correspond to "one" any which way you turn it.

$array = array( 'one' =>'value', 'two' => 'value2' );
 
$allKeys = array_keys($array);
echo $allKeys[0];

Which will output:

one

If you only plan to work with one key in particular, you may accomplish this with a single line without having to store an array for all of the keys:

echo array_keys($array)[$i];

Or if you need it in a loop

foreach ($array as $key => $value)
{
    echo $key . ':' . $value . "\n";
}
//Result: 
//one:value
//two:value2

$array = array( 'one' =>'value', 'two' => 'value2' );
$keys  = array_keys($array);
echo $keys[0]; // one
echo $keys[1]; // two

You might do it this way:

function asoccArrayValueWithNumKey(&$arr, $key) {
   if (!(count($arr) > $key)) return false;
   reset($array);
   $aux   = -1;
   $found = false;
   while (($auxKey = key($array)) && !$found) {
      $aux++;
      $found = ($aux == $key);
   }
   if ($found) return $array[$auxKey];
   else return false;
}

$val = asoccArrayValueWithNumKey($array, 0);
$val = asoccArrayValueWithNumKey($array, 1);
etc...

Haven't tryed the code, but i'm pretty sure it will work.

Good luck!

The key function helped me and is very simple:

> The key() function simply returns the key of the array element that's > currently being pointed to by the internal pointer. It does not move > the pointer in any way. If the internal pointer points beyond the end > of the elements list or the array is empty, key() returns NULL.

Example:

<?php
    $array = array(
        'fruit1' => 'apple',
        'fruit2' => 'orange',
        'fruit3' => 'grape',
        'fruit4' => 'apple',
        'fruit5' => 'apple');

    // this cycle echoes all associative array
    // key where value equals "apple"
    while ($fruit_name = current($array)) {
        if ($fruit_name == 'apple') {
            echo key($array).'<br />';
        }
        next($array);
    }
?>

The above example will output:

fruit1<br />
fruit4<br />
fruit5<br />

If it is the first element, i.e. $array[0], you can try:

echo key($array);

If it is the second element, i.e. $array[1], you can try:

next($array);
echo key($array);

I think this method is should be used when required element is the first, second or at most third element of the array. For other cases, loops should be used otherwise code readability decreases.

One more example:

Get the most frequent occurrence(s) in an array:

PHP >= 7.3:

$ php --version
PHP 7.4.3 (cli) (built: Oct  6 2020 15:47:56) ( NTS )
Copyright (c) The PHP Group
Zend Engine v3.4.0, Copyright (c) Zend Technologies
    with Zend OPcache v7.4.3, Copyright (c), by Zend Technologies

$ php -a
Interactive mode enabled

php > $a = array_count_values(array('abc','abc','def','def','def'));
php > var_dump($a);
array(2) {
  ["abc"]=>
  int(2)
  ["def"]=>
  int(3)
}
php > arsort($a);
php > var_dump($a);
array(2) {
  ["def"]=>
  int(3)
  ["abc"]=>
  int(2)
}
php > var_dump(array_key_first($a));
string(3) "def"
php > var_dump(array_keys($a)[1]);
string(3) "abc"

If you have the key, you can easily query the value (= the frequency).

just posting another solution for those that array_keys() is not working

$myAssociativeArray = [
  'name' => 'sun',
  'age' => 21
);

$arrayKeys = [];
foreach($myAssociativeArray as $key => $val){
    array_push($arrayKeys, $key);
}

print_r($arrayKeys)

// ['name', 'age']

Expanding on Ram Dane's answer, the key function is an alternative way to get the key of the current index of the array. You can create the following function,

    function get_key($array, $index){
      $idx=0;
      while($idx!=$index  && next($array)) $idx++;
      if($idx==$index) return key($array);
      else return '';
    }