prev

(PHP 4, PHP 5)

prevRewind the internal array pointer

Description

mixed prev ( array &$array )

Rewind the internal array pointer.

prev() behaves just like next(), except it rewinds the internal array pointer one place instead of advancing it.

Parameters

array

The input array.

Return Values

Returns the array value in the previous place that's pointed to by the internal array pointer, or FALSE if there are no more elements.

Examples

Example #1 Example use of prev() and friends

<?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';
?>

Notes

Warning

This function may return Boolean FALSE, but may also return a non-Boolean value which evaluates to FALSE. Please read the section on Booleans for more information. Use the === operator for testing the return value of this function.

Note: You won't be able to distinguish the beginning of an array from a boolean FALSE element. To properly traverse an array which may contain FALSE elements, see the each() function.

See Also

  • current() - Return the current element in an array
  • end() - Set the internal pointer of an array to its last element
  • next() - Advance the internal array pointer of an array
  • reset() - Set the internal pointer of an array to its first element
  • each() - Return the current key and value pair from an array and advance the array cursor

Коментарии

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);
}

?>
2009-05-29 15:06:28
http://php5.kiev.ua/manual/ru/function.prev.html
Автор:
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$colorlongtrue);
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$colorlongtrue);
    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;
    } 
}
?>
2014-03-31 04:17:54
http://php5.kiev.ua/manual/ru/function.prev.html
Автор:
Function to get element in array, that goes previous your key or false if it not exeists or key doesn't isset in array.

<?php

function 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;
}
2019-09-05 17:56:14
http://php5.kiev.ua/manual/ru/function.prev.html

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