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prev将数组的内部指针倒回一位

说明

prev(array|object &$array): mixed

将数组的内部指针倒回一位。

prev()next() 的行为类似,只除了它将内部指针倒回一位而不是前移一位。

参数

array

The input array.

返回值

返回数组内部指针指向的前一个单元的值,或当没有更多单元时返回 false

警告

此函数可能返回布尔值 false,但也可能返回等同于 false 的非布尔值。请阅读 布尔类型章节以获取更多信息。应使用 === 运算符来测试此函数的返回值。

更新日志

版本 说明
8.1.0 弃用在 object 上调用此函数。 要么首先使用 get_mangled_object_vars()object 转换为 array,要么使用实现 Iterator 的类提供的方法,例如 ArrayIterator
7.4.0 SPL 类的实例现在被视为没有属性的空对象,而不是调用与此函数同名的 Iterator 方法。

示例

示例 #1 prev() 及相关函数用法示例

<?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';
?>

注释

警告

此函数可能返回布尔值 false,但也可能返回等同于 false 的非布尔值。请阅读 布尔类型章节以获取更多信息。应使用 === 运算符来测试此函数的返回值。

注意: 很难区分是遇到 boolean false 单元还是遇到了数组的开头。 需要用 key() 检查 prev() 数组, 是否为 null 来作区分。

参见

  • current() - 返回数组中的当前值
  • end() - 将数组的内部指针指向最后一个单元
  • next() - 将数组中的内部指针向前移动一位
  • reset() - 将数组的内部指针指向第一个单元
  • each() - 返回数组中当前的键/值对并将数组指针向前移动一步

添加备注

用户贡献的备注 3 notes

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0
MicroVB INC
10 years 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
soapergem at gmail dot com
15 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
-2
Mikhail
5 years ago
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;
}
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