How to remove duplicates from php array

How to remove duplicate values ​​from a php array: First create a PHP sample file; then define an array; and finally use the "array_unique($arr);" method to remove duplicates from the elements in the array.

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1. Use the array_unique method to deduplicate

To deduplicate array elements, we generally use the array_unique method, use this Method can remove duplicate elements from an array.

<?php
$arr = array(1,1,2,3,3,3,4,4,5,6,6,7,8,8,9,9,9);
$arr = array_unique($arr);
$arr = array_values($arr);
print_r($arr);?>

Output:

Array(
    [0] => 1
    [1] => 2
    [2] => 3
    [3] => 4
    [4] => 5
    [5] => 6
    [6] => 7
    [7] => 8
    [8] => 9)

After deduplication, the key values ​​will be out of order. You can use array_values ​​to reorder the key values.

2. Use array_unique method to remove duplicates for efficiency

<?php
$arr = array();

// 创建100000个随机元素的数组
for($i=0; $i<100000; $i++){
    $arr[] = mt_rand(1,99);
}

// 记录开始时间
$starttime = getMicrotime();

// 去重
$arr = array_unique($arr);

// 记录结束时间
$endtime = getMicrotime();

$arr = array_values($arr);

echo &#39;unique count:&#39;.count($arr).&#39;<br>&#39;;
echo &#39;run time:&#39;.(float)(($endtime-$starttime)*1000).&#39;ms<br>&#39;;
echo &#39;use memory:&#39;.getUseMemory();

/**
 * 获取使用内存
 * @return float
 */
function getUseMemory(){
    $use_memory = round(memory_get_usage(true)/1024,2).&#39;kb&#39;;
    return $use_memory;
}

/**
 * 获取microtime
 * @return float
 */
function getMicrotime(){
    list($usec, $sec) = explode(&#39; &#39;, microtime());
    return (float)$usec + (float)$sec;
}
?>

unique count:99

run time:653.39303016663ms
use memory:5120kb

Use the

array_unique method to remove duplicates. The running time takes about 650ms and the memory usage is about 5m

3. Faster array deduplication method

php has a key-value exchange method array_flip. We can use this method to deduplicate. Because of key-value exchange, the original duplicate values ​​will become for the same key.

Then perform a key-value exchange, and exchange the keys and values ​​back to complete the deduplication.

<?php
$arr = array();

// 创建100000个随机元素的数组
for($i=0; $i<100000; $i++){
    $arr[] = mt_rand(1,99);
}

// 记录开始时间
$starttime = getMicrotime();

// 使用键值互换去重
$arr = array_flip($arr);
$arr = array_flip($arr);

// 记录结束时间
$endtime = getMicrotime();

$arr = array_values($arr);

echo &#39;unique count:&#39;.count($arr).&#39;<br>&#39;;
echo &#39;run time:&#39;.(float)(($endtime-$starttime)*1000).&#39;ms<br>&#39;;
echo &#39;use memory:&#39;.getUseMemory();

/**
 * 获取使用内存
 * @return float
 */
function getUseMemory(){
    $use_memory = round(memory_get_usage(true)/1024,2).&#39;kb&#39;;
    return $use_memory;
}

/**
 * 获取microtime
 * @return float
 */
function getMicrotime(){
    list($usec, $sec) = explode(&#39; &#39;, microtime());
    return (float)$usec + (float)$sec;
}
?>

unique count:99

run time:12.840032577515ms
use memory:768kb

Use

array_flip method to remove duplicates, the running time takes about 18ms, the memory usage is about 2m

. Therefore, using the

array_flip method to remove duplicates takes longer than using the array_unique method. The running time is 98%, memory usage reduced4/5;

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