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php - array_shift but preserve keys

My array looks like this:

$arValues = array( 345 => "jhdrfr", 534 => "jhdrffr", 673 => "jhrffr", 234 => "jfrhfr" );

How can I remove the first element of an array, but preserve the numeric keys? Since array_shift changes my integer key values to 0, 1, 2, ....

I tried using unset( $arValues[ $first ] ); reset( $arValues ); to continue using the second element (now first), but it returns false.

How can I achieve this?

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reset( $a );
unset( $a[ key($a)]);

A bit more useful version:

// rewinds array's internal pointer to the first element
// and returns the value of the first array element. 
$value = reset( $a );

// returns the index element of the current array position
$key   = key( $a );

unset( $a[ $key ]);

Functions:

// returns value
function array_shift_assoc( &$arr ){
  $val = reset( $arr );
  unset( $arr[ key( $arr ) ] );
  return $val; 
}

// returns [ key, value ]
function array_shift_assoc_kv( &$arr ){
  $val = reset( $arr );
  $key = key( $arr );
  $ret = array( $key => $val );
  unset( $arr[ $key ] );
  return $ret; 
}

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