How to improve efficiency of finding array elements in PHP

This article mainly introduces how to improve the efficiency of searching array elements in PHP, which has a good reference value. Interested friends can refer to it, I hope it will be helpful to everyone.

1.php in_array method description

PHP will generally use the in_array method to find whether an array element exists.

bool in_array ( mixed $needle , array $haystack [, bool $strict = FALSE ] )

Parameter description:

needle

The value to be searched. If needle is a string, the comparison is case-sensitive.

haystack

Array used for comparison

strict

If the value of the third parameter strict is TRUE, the in_array() function will also check whether the type of needle is the same as that in haystack

Return value

Returns TRUE if needle is found, otherwise returns FALSE.

2. The efficiency of finding elements in in_array

When the comparison array haystack is large, the efficiency of in_array will be very low

Example: Use in_array to perform 1000 comparisons on an array of 100,000 elements

##

<?php
$arr = array();

// 创建10万个元素的数组
for($i=0; $i<100000; $i++){
 $arr[] = $i;
}

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

// 随机创建1000个数字使用in_array比较
for($j=0; $j<1000; $j++){
 $str = mt_rand(1,99999);
 in_array($str, $arr);
}

// 记录结束时间
$endtime = getMicrotime();

echo &#39;run time:&#39;.(float)(($endtime-$starttime)*1000).&#39;ms<br>&#39;;
/**
 * 获取microtime
 * @return float
 */
function getMicrotime(){
 list($usec, $sec) = explode(&#39; &#39;, microtime());
 return (float)$usec + (float)$sec;
}
?>

run time:

2003.6449432373ms

Use

in_array to determine whether an element exists. Compare 1000 times in an array of 100,000 elements. The running time takes about 2 seconds

3. Method to improve the efficiency of finding elements

We can first use

array_flip to perform key-value exchange, and then use the isset method to determine the element Whether it exists, this can improve efficiency.

Example: Use array_flip to first exchange key values, then use the isset method to judge, and compare 1000 times in an array of 100,000 elements

<?php
$arr = array();

// 创建10万个元素的数组
for($i=0; $i<100000; $i++){
 $arr[] = $i;
}

// 键值互换
$arr = array_flip($arr);

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

// 随机创建1000个数字使用isset比较
for($j=0; $j<1000; $j++){
 $str = mt_rand(1,99999);
 isset($arr[$str]);
}

// 记录结束时间
$endtime = getMicrotime();

echo &#39;run time:&#39;.(float)(($endtime-$starttime)*1000).&#39;ms<br>&#39;;
/**
 * 获取microtime
 * @return float
 */
function getMicrotime(){
 list($usec, $sec) = explode(&#39; &#39;, microtime());
 return (float)$usec + (float)$sec;
}
?>

run time:

1.2781620025635ms

Use

array_flip and isset to determine the element Does it exist, comparing 1000 times in an array of 100,000 elements, the run time takes about 1.2 milliseconds

So, for comparing large arrays, use array_flip# The ## and isset methods are much more efficient than in_array.

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