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prev내부 배열 포인터를 후진

설명

mixed prev ( array &$array )

내부 배열 포인터를 후진합니다.

prev()는 내부 배열 포인터를 한칸 전진시키는 대신 후진하는 점을 제외하면 next()처럼 작동합니다.

인수

array

입력 배열.

반환값

내부 배열 포인터가 가리키는 이전 위치의 배열 값을 반환하거나, 더 이상 원소가 없을 경우 FALSE를 반환합니다.

예제

Example #1 prev() 용례와 관련 함수

<?php
$transport 
= array('foot''bike''car''plane');
$mode current($transport); // $mode = 'foot';
$mode next($transport);    // $mode = 'bike';
$mode next($transport);    // $mode = 'car';
$mode prev($transport);    // $mode = 'bike';
$mode end($transport);     // $mode = 'plane';
?>

주의

Warning

이 함수는 논리 FALSE를 반환하지만, 0이나 "" 등, 논리 FALSE로 취급할 수 있는 다른 값을 반환할 수 있습니다. 자세한 정보는 논리형 섹션을 참고하십시오. 이 함수의 반환값을 확인하려면 === 연산자를 이용하십시오.

Note: 배열의 끝과 boolean FALSE 원소를 구별할 수 없습니다. FALSE 원소를 가지는 배열을 올바르게 따라가려면, each()를 참고하십시오.

참고

  • current() - 배열의 현재 원소를 반환
  • end() - 배열 내부 포인터가 마지막 원소를 가리키게 설정
  • next() - 배열의 내부 배열 포인터를 전진
  • reset() - 배열의 내부 포인터를 첫 원소로 설정
  • each() - 배열에서 현재 키와 값 쌍을 반환하고 배열 커서를 전진

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User Contributed Notes 3 notes

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3
soapergem at gmail dot com
4 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
0
MicroVB INC
18 days 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';

    }

?>
up
0
MicroVB INC
18 days 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;
    } 
}
?>
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