PHP - 如何从数组中获取最后一个元素之前的元素？

PHP - How to get the element before the last element from an array?

提问by Manny Calavera

How can I get the element before the last element from an array in PHP5 ?

如何从 PHP5 中的数组中获取最后一个元素之前的元素？

回答by Erik

This will work even on this array:

这甚至可以在这个数组上工作：

$array[0] = "hello";
$array[5] = "how";
$array[9] = "are";

end($array);
echo prev($array); // will print "how"

The other solutions using count() are assuming that the indexes of your array go in order; by using end and prev to move the array pointer, you get the actual values. Try using the count() method on the array above and it will fail.

使用 count() 的其他解决方案假设数组的索引按顺序排列；通过使用 end 和 prev 移动数组指针，您可以获得实际值。尝试在上面的数组上使用 count() 方法，它会失败。

回答by Notinlist

$array[count($array)-2]

It should be a numerically indexed array (from zero). You should have at least 2 elements for this to work. (obviously)

它应该是一个数字索引数组（从零开始）。你应该至少有 2 个元素才能工作。（明显地）

回答by DevAnimal

As for me pretty tiny solution

至于我，非常小的解决方案

end($array);
echo prev($array);

回答by James Wheare

array_slice takes a negative offset as the second argument. This will give you a single item array containing the second last item:

array_slice 将负偏移量作为第二个参数。这将为您提供一个包含倒数第二个项目的单个项目数组：

$arr = array(1,2,3,4,5,6);
array_slice($arr, -2, 1);

If you just want the single value on it's own you have several options. If you don't mind using an intermediate variable you can then just get the first value with [0] or call array_pop or array_shift, they both need a variable passed by reference or you'll get warnings in strict mode.

如果您只想要它自己的单个值，您有多种选择。如果您不介意使用中间变量，则可以使用 [0] 或调用 array_pop 或 array_shift 获取第一个值，它们都需要通过引用传递的变量，否则您将在严格模式下收到警告。

Or you could just use array_sum or array_product, which is a bit hacky but works fine for single item arrays.

或者你可以只使用 array_sum 或 array_product，这有点 hacky 但适用于单项数组。

回答by Yada

A method that will work for both associativearray and numeric array is to use array_pop()to pop the element off the end of array.

一种适用于关联数组和数值数组的方法是使用array_pop()从数组末尾弹出元素。

$last = array_pop($array);
$second_last = array_pop($array);

// put back the last
array_push($array, $last);

回答by TarranJones

All arrays have an "internal array pointer"which points to the current array element, PHP has several functions which allow you to navigate through the array and view the current elements key and value.

所有数组都有一个指向当前数组元素的“内部数组指针”，PHP 有几个函数可以让你在数组中导航并查看当前元素的键和值。

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

• end()- 将数组的内部指针设置为其最后一个元素
• reset()- 将数组的内部指针设置为其第一个元素
• prev()- 倒带内部数组指针
• next()- 推进数组的内部数组指针
• current()- 返回数组中的当前元素
• key()- 从数组中获取一个键
• each()- 从数组中返回当前的键值对并前进数组光标

These functions work whether the array is empty, sequential or associative and as an array has not been specified in the example i've assumed this must work with any array.

无论数组是空的、顺序的还是关联的，这些函数都可以工作，并且由于示例中未指定数组，我假设这必须适用于任何数组。

$array = array(
    'before_last' => false,
    'last' => false,
);

end($array); /* 
- set pointer to last element -> $array['last']
- return new current element value if it exists, -> false
- else return FALSE 
*/

prev($array); /* 
- set pointer one place before current pointer -> $array['before_last']
- return new current element value if it exists, -> false
- else return FALSE 
*/

if(!is_null(key($array)){ /* 
- return current element key if it exists -> "before_last"
- else return NULL
*/
    $before_last_element_value = current($array); /* 
    - return current element value if it exists, -> false
    - else return FALSE 
    */
}

As you can see the expected result (false) and the result for a nonexistent element is the same (FALSE) so you cannot check whether an element exists using the returned element value, an element key is different.

如您所见，预期结果 ( false) 和不存在元素的结果相同 ( FALSE)，因此您无法使用返回的元素值检查元素是否存在，元素键不同。

The key can either be an integeror a string. The value can be of any type. source

键可以是整数或字符串。该值可以是任何type. 来源

The key()returns the value of the current key if the element exists otherwise it will return NULL. A valid key can never be NULL so if null is returned we can determine that the element does not exist.

该key()如果元素存在，否则将返回NULL返回当前键的值。有效的键永远不能为 NULL，因此如果返回 null，我们可以确定该元素不存在。

回答by Darshana

// Indexed based array
$test = array('a','b','c','d','e');
$count = count($test);
print $test[$count-2];

// Associative Array
$months = array(
         'jan'=>'January', 
         'feb' => 'february', 
         'mar' => 'March', 
         'apr' => 'April'
    );

$keys = array_keys($months);
$count = count($keys);
print $keys[$count-2];