php只返回数组中的重复条目

I want to retrieve all duplicated entries from a array. Is this possible in PHP?

我想从数组中检索所有重复的条目。这可能在PHP？

array(
    1 => '1233',
    2 => '12334',
    3 => 'Hello',
    4 => 'hello',
    5 => 'U'
);

I want to return an array with just the duplicate value: “hello”.

我想返回一个只有重复值的数组：“hello”。

Desired output array:

期望的输出数组：

array(
    1 => 'Hello',
    2 => 'hello'
);

6 个解决方案

#1

You will need to make your function case insensitive to get the "Hello" => "hello" result you are looking for, try this method:

您将需要使您的函数大小写不敏感以获得您正在寻找的“Hello”=>“hello”结果，请尝试以下方法：

$arr = array(1=>'1233',2=>'12334',3 =>'Hello' ,4=>'hello', 5=>'U');

// Convert every value to uppercase, and remove duplicate values
$withoutDuplicates = array_unique(array_map("strtoupper", $arr));

// The difference in the original array, and the $withoutDuplicates array
// will be the duplicate values
$duplicates = array_diff($arr, $withoutDuplicates);
print_r($duplicates);

Output is:

输出是：

Array
(
[3] => Hello
[4] => hello
)

Edit by @AlixAxel:

由@AlixAxel编辑：

This answer is very misleading. It only works in this specific condition. This counter-example:

这个答案非常具有误导性。它只适用于这种特定条件。这个反例：

$arr = array(1=>'1233',2=>'12334',3 =>'Hello' ,4=>'HELLO', 5=>'U');

Fails miserably. Also, this is not the way to keep duplicates:

悲惨地失败了。此外，这不是保持重复的方法：

array_diff($arr, array_unique($arr));

Since one of the duplicated values will be in array_unique, and then chopped off by array_diff.

由于其中一个重复值将在array_unique中，然后由array_diff切断。

Edit by @RyanDay:

由@RyanDay编辑：

So look at @Srikanth's or @Bucabay's answer, which work for all cases (look for case insensitive in Bucabay's), not just the test data specified in the question.

那么看看@ Srikanth或@ Bucabay的答案，它适用于所有情况（在Bucabay中查找不区分大小写），而不仅仅是问题中指定的测试数据。

#2

<?php
function array_not_unique($raw_array) {
    $dupes = array();
    natcasesort($raw_array);
    reset($raw_array);

    $old_key   = NULL;
    $old_value = NULL;
    foreach ($raw_array as $key => $value) {
        if ($value === NULL) { continue; }
        if (strcasecmp($old_value, $value) === 0) {
            $dupes[$old_key] = $old_value;
            $dupes[$key]     = $value;
        }
        $old_value = $value;
        $old_key   = $key;
    }
    return $dupes;
}

$raw_array    = array();
$raw_array[1] = 'abc@xyz.com';
$raw_array[2] = 'def@xyz.com';
$raw_array[3] = 'ghi@xyz.com';
$raw_array[4] = 'abc@xyz.com'; // Duplicate

$common_stuff = array_not_unique($raw_array);
var_dump($common_stuff);

#3

function get_duplicates ($array) {
    return array_unique( array_diff_assoc( $array, array_unique( $array ) ) );
}

#4

function array_not_unique($raw_array) {
    $dupes = array();
    natcasesort($raw_array);
    reset($raw_array);

    $old_key   = NULL;
    $old_value = NULL;
    foreach ($raw_array as $key => $value) {
        if ($value === NULL) { continue; }
        if (strcasecmp($old_value, $value) === 0) {
            $dupes[$old_key] = $old_value;
            $dupes[$key]     = $value;
        }
        $old_value = $value;
        $old_key   = $key;
    } return $dupes;
}

What Srikanth (john) added but with the case insensitive comparison.

Srikanth（约翰）添加了什么，但不区分大小写。

#5

This is the correct way to do it (case-sensitive):

这是正确的方法（区分大小写）：

array_intersect($arr, array_unique(array_diff_key($arr, array_unique($arr))));

And a case-insensitive solution:

并且不区分大小写的解决方案：

$iArr = array_map('strtolower', $arr);
$iArr = array_intersect($iArr, array_unique(array_diff_key($iArr, array_unique($iArr))));

array_intersect_key($arr, $iArr);

But @Srikanth answer is more efficient (actually, it's the only one that works correctly besides this one).

但是@Srikanth的答案更有效率（实际上，除了这个之外，它是唯一正常工作的答案）。

#6

Try:

尝试：

$arr2 = array_diff_key($arr, array_unique($arr));

case insensitive:

不区分大小写：

array_diff_key($arr, array_unique(array_map('strtolower', $arr)));

#1