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(PHP 4, PHP 5)
prev — Передвинуть внутренний указатель массива на одну позицию назад
Описание
Возвращает значение элемента массива, находящегося на позиции, предыдущей по отношению к позиции, в которой находится его внутренний указатель или FALSE, если достигнут конец массива.
Внимание
Если массив содержит пустые или равные 0 элементы, функция возвратит FALSE для этих элементов. Для того, чтобы правильно просматривать массивы, содержащие пустые элементы, используйте функцию each().
prev() ведёт себя подобно next(), за исключением того, что она передвигает внутренний указатель массива на одну позицию назад, а не вперёд.
Пример #1 Пример использования prev() и друзей
<?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); // $mode = 'plane';
?>
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Коментарии
Here's a slight revision to xmlich02's backwards iteration example. The problem with his/her example is that it will halt if any of the array elements are boolean false, while this version will not.
<?php
end($ar);
while ( !is_null($key = key($ar)) ) {
$val = current($ar);
echo "{$key} => {$val}\n";
prev($ar);
}
?>
This function searches for the closest element in an array by key value, and returns the key/value pair, or false if not found.
<?php
function nearest($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 #" . $color;
}
}
?>
Some corrections to the previous function.
- When prev() and next() distance is now calculated properly returning the 'closer' one.
- When exact is false, and an item exists with the key searched for, it now returns that entry instead of next/prev closest
- At ends of the array, sometimes when moving past using next() or prev(), it caused results to die. This was corrected.
- Added field to result stating whether the match was 'exact' ('exact'=>true), or nearest ('exact'=>false)
<?php
function nearest($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';
}
?>
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;
}