我有一个foreach循环，我想看看循环中是否有下一个元素，所以我可以将当前元素与下一个元素进行比较。我怎样才能做到这一点？我已经阅读了当前和下一个功能，但我无法弄清楚如何使用它们。
提前致谢
答案 0 :(得分：31)
一种独特的方法是反转数组和然后循环。这也适用于非数字索引的数组：
$items = array(
'one' => 'two',
'two' => 'two',
'three' => 'three'
);
$backwards = array_reverse($items);
$last_item = NULL;
foreach ($backwards as $current_item) {
if ($last_item === $current_item) {
// they match
}
$last_item = $current_item;
}
如果您仍然对使用current和next函数感兴趣，可以这样做：
$items = array('two', 'two', 'three');
$length = count($items);
for($i = 0; $i < $length - 1; ++$i) {
if (current($items) === next($items)) {
// they match
}
}
＃2可能是最好的解决方案。注意，$i < $length - 1;将在比较数组中的最后两项后停止循环。我把它放在循环中以显示示例。您应该只计算$length = count($items) - 1;
答案 1 :(得分：14)
您可以使用while循环而不是foreach：
while ($current = current($array) )
{
$next = next($array);
if (false !== $next && $next == $current)
{
//do something with $current
}
}
答案 2 :(得分：10)
正如php.net/foreach所指出的那样：
除非引用了数组，否则foreach将对指定数组的副本进行操作，而不是对数组本身进行操作。 foreach对数组指针有一些副作用。不要在foreach期间或之后依赖数组指针而不重置它。
换句话说 - 做你要做的事并不是一个好主意。或许最好与某人讨论你为什么要这样做，看看是否有更好的解决方案？如果您没有任何其他可用资源，请随时在irc.freenode.net上的## PHP中询问我们。
答案 3 :(得分：7)
如果索引是连续的：
foreach ($arr as $key => $val) {
if (isset($arr[$key+1])) {
echo $arr[$key+1]; // next element
} else {
// end of array reached
}
}
答案 4 :(得分：4)
如果用数字索引：
foreach ($foo as $key=>$var){
if($var==$foo[$key+1]){
echo 'current and next var are the same';
}
}
答案 5 :(得分：3)
一般解决方案可以是缓存迭代器。正确实现的缓存迭代器可以与任何迭代器一起使用，并节省内存。 PHP SPL有CachingIterator，但它很奇怪，功能非常有限。但是，您可以编写自己的前瞻迭代器，如下所示：
<?php
class NeighborIterator implements Iterator
{
protected $oInnerIterator;
protected $hasPrevious = false;
protected $previous = null;
protected $previousKey = null;
protected $hasCurrent = false;
protected $current = null;
protected $currentKey = null;
protected $hasNext = false;
protected $next = null;
protected $nextKey = null;
public function __construct(Iterator $oInnerIterator)
{
$this->oInnerIterator = $oInnerIterator;
}
public function current()
{
return $this->current;
}
public function key()
{
return $this->currentKey;
}
public function next()
{
if ($this->hasCurrent) {
$this->hasPrevious = true;
$this->previous = $this->current;
$this->previousKey = $this->currentKey;
$this->hasCurrent = $this->hasNext;
$this->current = $this->next;
$this->currentKey = $this->nextKey;
if ($this->hasNext) {
$this->oInnerIterator->next();
$this->hasNext = $this->oInnerIterator->valid();
if ($this->hasNext) {
$this->next = $this->oInnerIterator->current();
$this->nextKey = $this->oInnerIterator->key();
} else {
$this->next = null;
$this->nextKey = null;
}
}
}
}
public function rewind()
{
$this->hasPrevious = false;
$this->previous = null;
$this->previousKey = null;
$this->oInnerIterator->rewind();
$this->hasCurrent = $this->oInnerIterator->valid();
if ($this->hasCurrent) {
$this->current = $this->oInnerIterator->current();
$this->currentKey = $this->oInnerIterator->key();
$this->oInnerIterator->next();
$this->hasNext = $this->oInnerIterator->valid();
if ($this->hasNext) {
$this->next = $this->oInnerIterator->current();
$this->nextKey = $this->oInnerIterator->key();
} else {
$this->next = null;
$this->nextKey = null;
}
} else {
$this->current = null;
$this->currentKey = null;
$this->hasNext = false;
$this->next = null;
$this->nextKey = null;
}
}
public function valid()
{
return $this->hasCurrent;
}
public function hasNext()
{
return $this->hasNext;
}
public function getNext()
{
return $this->next;
}
public function getNextKey()
{
return $this->nextKey;
}
public function hasPrevious()
{
return $this->hasPrevious;
}
public function getPrevious()
{
return $this->previous;
}
public function getPreviousKey()
{
return $this->previousKey;
}
}
header("Content-type: text/plain; charset=utf-8");
$arr = [
"a" => "alma",
"b" => "banan",
"c" => "cseresznye",
"d" => "dio",
"e" => "eper",
];
$oNeighborIterator = new NeighborIterator(new ArrayIterator($arr));
foreach ($oNeighborIterator as $key => $value) {
// you can get previous and next values:
if (!$oNeighborIterator->hasPrevious()) {
echo "{FIRST}\n";
}
echo $oNeighborIterator->getPreviousKey() . " => " . $oNeighborIterator->getPrevious() . " -----> ";
echo "[ " . $key . " => " . $value . " ] -----> ";
echo $oNeighborIterator->getNextKey() . " => " . $oNeighborIterator->getNext() . "\n";
if (!$oNeighborIterator->hasNext()) {
echo "{LAST}\n";
}
}
答案 6 :(得分：2)
您可以在foreach之前获取数组的键，然后使用计数器检查下一个元素，如：
//$arr is the array you wish to cycle through
$keys = array_keys($arr);
$num_keys = count($keys);
$i = 1;
foreach ($arr as $a)
{
if ($i < $num_keys && $arr[$keys[$i]] == $a)
{
// we have a match
}
$i++;
}
这适用于简单数组（例如array(1,2,3)）和键控数组（例如array('first'=>1, 'second'=>2, 'thrid'=>3)）。
答案 7 :(得分：1)
php中的foreach循环将迭代原始数组的副本，使next()和prev()函数无效。如果你有一个关联数组并需要获取下一个项目，你可以改为迭代数组键：
foreach (array_keys($items) as $index => $key) {
// first, get current item
$item = $items[$key];
// now get next item in array
$next = $items[array_keys($items)[$index + 1]];
}
由于生成的键数组本身具有连续索引，因此您可以使用它来访问原始数组。
请注意最后一次迭代$next为null，因为最后一次之后没有下一个项目。访问不存在的数组键将引发php通知。为避免这种情况，要么：
$next index + 1的密钥是否与array_key_exists() 使用方法2，完整的foreach可能如下所示：
foreach (array_keys($items) as $index => $key) {
// first, get current item
$item = $items[$key];
// now get next item in array
$next = null;
if (array_key_exists($index + 1, array_keys($items))) {
$next = $items[array_keys($items)[$index + 1]];
}
}
答案 8 :(得分：1)
您可以获取键/值和索引
<?php
$a = array(
'key1'=>'value1',
'key2'=>'value2',
'key3'=>'value3',
'key4'=>'value4',
'key5'=>'value5'
);
$keys = array_keys($a);
foreach(array_keys($keys) as $index ){
$current_key = current($keys); // or $current_key = $keys[$index];
$current_value = $a[$current_key]; // or $current_value = $a[$keys[$index]];
$next_key = next($keys);
$next_value = $a[$next_key] ?? null; // for php version >= 7.0
echo "{$index}: current = ({$current_key} => {$current_value}); next = ({$next_key} => {$next_value})\n";
}
结果：
0: current = (key1 => value1); next = (key2 => value2)
1: current = (key2 => value2); next = (key3 => value3)
2: current = (key3 => value3); next = (key4 => value4)
3: current = (key4 => value4); next = (key5 => value5)
4: current = (key5 => value5); next = ( => )