prev

This function searches for the closest element in an array by key value, and returns the key/value pair, or false if not found.<?phpfunction nearest($array, $value, $exact=false) {        // Initialize Variables    $next = false;    $prev = false;    $return = false;        if(!isset($array[$value]) && !$exact) {        // Insert element that doesn't exist so nearest can be found        $array[$value] = '-';    }        if($exact && isset($array[$value])) {                // If exact match found, and searching for exact (not nearest), return result.        $return = Array($value=>$array[$value]);    } else {            // Sort array so injected record is near relative numerics        ksort($array); // Sort array on key                // Loop through array until match is found, then set $prev and $next to the respective keys if exist        while ( !is_null($key = key($array)) ) {            $val = current($array);            if($key == $value) {                prev($array); // Get entry before this one                $prev = key($array);                next($array);         // Skip current entry as this was what we were looking for nearest to                next($array); // Get entry after this one                $next = key($array);                break;            }            next($array);        }        if($prev && $next) {            if(($long - $prev) > ($next - $long)) {                                 // Previous is closer                $return = Array($prev=>$array[$prev]);            } else {                                 // Next is closer                $return = Array($next=>$array[$next]);            }        } elseif ($prev || $next) {            if($prev) {                                 // Only Previous exists                $return = Array($prev=>$array[$prev]);            } elseif ($next) {                                 // Only Next exists                $return = Array($next=>$array[$next]);            }        }    }        // Return resulting Array().   $return is false if nothing matches the closest conditions, or if exact is specified and key does not exist.            return $return;}?>Example usage (to lookup the closest color in an array)<?php$mycolors= Array(    5001046=>'Abbey',    1774596=>'Acadia',    8171681=>'Acapulco',    6970651=>'Acorn',    13238245=>'Aero Blue',    7423635=>'Affair',    8803850=>'Afghan Tan',    13943976=>'Akaroa',    16777215=>'Alabaster',    16116179=>'Albescent White',    10176259=>'Alert Tan',    30371=>'Allports');// Color to search for in Hex$color = 'C0C0C0';// Convert Hex to Long to compare with array() keys$colorlong = base_convert($color,16,10);// Check for an exact match$result = nearest($mycolors, $colorlong, true);if($result) {    echo "An exact match was found for #" . $color . " which is called '" . $result[key($result)] . "'";} else {    echo "No exact match was found";}if(!$result) {    // Check for closest match    $result = nearest($mycolors, $colorlong, true);    if($result) {        // Match found        echo "The closest match for #" . $color . " is #" . base_convert(key($result),10,16) . " which is called '" . $result[key($result)] . "'";    } else {        // No match found        echo "No match was found for #" . $color;    }  }?>

Here's a slight revision to xmlich02's backwards iteration example. The problem with his/her example is that it will halt if any of the array elements are boolean false, while this version will not.<?phpend($ar);while ( !is_null($key = key($ar)) ) {    $val = current($ar);    echo "{$key} => {$val}\n";    prev($ar);}?>

Function to get element in array, that goes previous your key or false if it not exeists or key doesn't isset in array.<?phpfunction previousElement(array $array, $currentKey){    if (!isset($array[$currentKey])) {        return false;    }    end($array);    do {        $key = array_search(current($array), $array);        $previousElement = prev($array);    }    while ($key != $currentKey);    return $previousElement;}