prev

(PHP 4, PHP 5)

prevSetzt den internen Zeiger eines Arrays um ein Element zurück

Beschreibung

mixed prev ( array &$array )

Setzt den internen Arrayzeiger ein Element zurück.

prev() verhält sich genauso wie next(), abgesehen davon, dass es den Zeiger ein Element nach hinten bewegt, nicht nach vorne.

Parameter-Liste

array

Das Array, dessen Zeiger verschoben werden soll.

Rückgabewerte

Liefert den Wert des Elements vor der Position des Arrays, auf die der interne Zeiger gerade zeigt. Sind keine Elemente mehr vorhanden, wird FALSE zurückgegeben.

Beispiele

Beispiel #1 Beispiel für die Verwendung von prev() und anderen

<?php
$transport 
= array('zu Fuß''Fahrrad''Auto''Flugzeug');
$mode current($transport); // $mode = 'zu Fuß';
$mode next($transport);    // $mode = 'Fahrrad';
$mode next($transport);    // $mode = 'Auto';
$mode prev($transport);    // $mode = 'Fahrrad';
$mode end($transport);     // $mode = 'Flugzeug';
?>

Anmerkungen

Warnung

Diese Funktion kann sowohl das boolsche FALSE zurückliefern, als auch einen nicht-boolschen Wert, welcher zu FALSE ausgewertet wird. Weitere Informationen entnehmen Sie bitte dem Abschnitt über die boolschen Typen. Benutzen Sie deshalb den === Operator, um den Rückgabewert dieser Funktion zu überprüfen.

Hinweis: Es ist nicht möglich, den Anfang eines Arrays von einem boolean FALSE-Wert zu unterscheiden. Um ein Array, das FALSE-Elemente beinhalten könnte, korrekt zu durchlaufen werfen Sie bitte einen Blick auf die each()- Funktion.

Siehe auch

  • current() - Liefert das aktuelle Element eines Arrays
  • end() - Positioniert den internen Zeiger eines Arrays auf dessen letztes Element
  • next() - Rückt den internen Zeiger eines Arrays vor
  • reset() - Setzt den internen Zeiger eines Arrays auf sein erstes Element
  • each() - Liefert das aktuelle Paar (Schlüssel und Wert) eines Arrays und rückt den Arrayzeiger vor

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User Contributed Notes 3 notes

up
2
soapergem at gmail dot com
5 years ago
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.

<?php

end
($ar);
while ( !
is_null($key = key($ar)) ) {
   
$val = current($ar);
    echo
"{$key} => {$val}\n";
   
prev($ar);
}

?>
up
1
MicroVB INC
8 months ago
This function searches for the closest element in an array by key value, and returns the key/value pair, or false if not found.

<?php
function 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;
    } 
}
?>
up
-1
MicroVB INC
8 months ago
Some corrections to the previous function.
- When prev() and next() distance is now calculated properly returning the 'closer' one.
- When exact is false, and an item exists with the key searched for, it now returns that entry instead of next/prev closest
- At ends of the array, sometimes when moving past using next() or prev(), it caused results to die. This was corrected.
- Added field to result stating whether the match was 'exact' ('exact'=>true), or nearest ('exact'=>false)

<?php
function nearest($array, $value, $exact=false) {
   
// Initialize Variables
   
$next = false;
   
$prev = false;
   
$return = false;

   
$arr_begin = false;
   
$arr_end = false;
       
   
$exact_match = false;
       
   
    if(
$exact && isset($array[$value])) {
       
// If exact match found, and searching for exact (not nearest), return result.
       
$return = Array($value=>$array[$value]);
       
$exact_match = true;
    } elseif (!
$exact && isset($array[$value])) {
       
// If exact match found, and searching for nearest, return result.
       
$return = Array($value=>$array[$value]);
       
$exact_match = true;
    } else {

        if(!isset(
$array[$value]) && !$exact) {
           
// Insert element that doesn't exist so nearest can be found
           
$array[$value] = '-';
        }
   
       
// Sort array so injected record is near relative numerics
       
ksort($array); // Sort array on key

        // Set start and end keys
       
$arr_begin = key($array);
       
end($array);
       
$arr_end = key($array);
       
reset($array);
       
       
// 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) {
                if(
$value <> $arr_begin) {
                   
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
               
               
if($value <> $arr_end) {
                   
next($array); // Get entry after this one
                   
$next = key($array);
                }
                break;
            }
           
next($array);
        }

        if(
$prev && $next) {
            if((
$value - $prev) < ($next - $value)) {
               
// 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.       
   
if($return) {
        return
$return+Array('exact'=>$exact_match);
    } else {
        return
false;
    }
}
?>

Just to clarify, this function will return either an Array() containing the $key=>$value pair of the result and 'exact'=>(bool) whether the match was exact or not.

To access the $key=>$value pair, can be done as follows :
<?php

    $result
= nearest( ... );  // Just here for clarification of the position for the code that follows.
    
   
if($result) {
       
// Output the Key
       
echo key($result);

       
// Output the Value
       
echo $result( key($result) );

       
// Output if exact match
       
if($result['exact']) {
            echo
'This was an EXACT match';
        } else {
            echo
'This result was found with fuzzy logic';
        }

    } else {

        echo
'No result found';

    }

?>
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