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Getting the next key in an array

Posted on 2005-05-16
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Last Modified: 2006-11-18
I have an array where the keys are numeric but not sequential, so its:

23, 354, 545, 2333 etc

I now have the value for a key, say 354 and I want to get the next key, in this case 545.

What is the best way to do this? Do I need to loop through the array, match the key and then get the next match. Is there a more efficient method?
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Question by:thepadders
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8 Comments
 
LVL 32

Expert Comment

by:ldbkutty
ID: 14014596
Since you need just the key - value pair, foreach loop will serve good:

$myKey = false;
foreach($my_array as $key=>$value)
{
     if($myKey) {
        echo "$key : $value";
        $myKey = false;
        // break;
     }
     if($value == YOUR_VALUE) {
        $myKey = true;
     }
}

If you want to get the key for a value, array_search ( http://www.php.net/array_search ) function is handy.
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LVL 11

Expert Comment

by:ZhaawZ
ID: 14014744
what about key(next($array)) ?
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Author Comment

by:thepadders
ID: 14014789
ZhaawZ,

How do you move the internal pointer of an array to a specific key?
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LVL 11

Accepted Solution

by:
ZhaawZ earned 2000 total points
ID: 14014813
$arr = array (
  23 => '1st',
  354 => '2nd',
  545 => '3rd',
  2333  => '4th'
);

reset($arr);
while ( key($arr) != 354 ) { next($arr); }
next($arr);
echo key($arr);
0
 

Author Comment

by:thepadders
ID: 14014853
Is that any different/better than the foreach method?
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LVL 32

Expert Comment

by:ldbkutty
ID: 14014931
Yes, foreach creates a copy of the array and loops through that copy. It is NOT as fast as ZhaawZ method. So go with it.
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LVL 10

Expert Comment

by:mensuck
ID: 14015826
Hi

I would just use the basic array functions with a loop, but when working with big array(s) it not very good when the key you are matching is at the end of the array! With big arrays use a preg_ function with implode! This way you don't need to use a loop or do 100(s) or even thousands of if(s) or repeated array function calls in that loop!

example...

<?

$arr = array ( 23 => '1st', 354 => '2nd', 545 => '3rd', 2333 => '4th' );

$key = 545;

if ( isset ( $arr[$key] ) )
{
      $next = preg_replace ( "!^.*?(" . $key . ")\|?(.*)\|?!", "\\2", implode ( '|', array_keys( $arr ) ) );

      if ( ! empty ( $next ) )
      {
            echo 'Next key: ' . $next . ' => ' . $arr[$next];
      }
      else
      {
            echo 'key: ' . $key . ', is the last element in array (arr) no next key';
      }
}
else
{
      echo $key . 'does not exit!';
}

?>

Suzanne
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LVL 49

Expert Comment

by:Roonaan
ID: 14016028
@Suzanne:

Wouldn't your method also load keys in subarrays?

Lets say we would have
array(1 => array("test" => 1, "test2"=>2), 2, 3, 4);

Your code would show us that "test2" is the next key following key "test", although array["test2"] does not work.

-r-
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