[英]PHP - array to 'unique'
I have an array that looks like the following: 我有一个看起来像下面的数组:
array(43197) {
[0]=> array(4) {
["id"]=> string(5) "10038"
["country"]=> string(7) "Andorra"
["city"]=> string(16) "Andorra la Vella"
["name"]=> string(25) "Andorra la Vella Heliport"
}
[1]=> array(4) {
["id"]=> string(5) "10040"
["country"]=> string(20) "United Arab Emirates"
["city"]=> string(17) "Abu Dhabi Emirate"
["name"]=> string(11) "Ras Sumeira"
}
[2]=> array(4) {
["id"]=> string(5) "10041"
["country"]=> string(20) "United Arab Emirates"
["city"]=> string(13) "Dubai Emirate"
["name"]=> string(27) "Burj al Arab Resort Helipad"
}
[3]=> array(4) {
["id"]=> string(5) "10042"
["country"]=> string(20) "United Arab Emirates"
["city"]=> string(13) "Dubai Emirate"
["name"]=> string(13) "Dubai Skydive"
}
[4]=> array(4) {
["id"]=> string(5) "14243"
["country"]=> string(20) "United Arab Emirates"
["city"]=> string(13) "Dubai Emirate"
["name"]=> string(15) "Dubai Creek SPB"
}
[5]=> array(4) {
["id"]=> string(5) "29266"
["country"]=> string(20) "United Arab Emirates"
["city"]=> string(17) "Abu Dhabi Emirate"
["name"]=> string(18) "Yas Island Airport"
}
...
}
Now I want to make this array 'unique' (to be able to create some select boxes later). 现在,我想使此数组“唯一”(以便以后可以创建一些选择框)。 I already have a function that works as expected... unfortunately it takes hours to complete with a very big array :(
我已经有一个可以按预期工作的函数...不幸的是,要花很长时间才能完成一个非常大的数组:(
Any ideas how to make this function faster? 任何想法如何使此功能更快?
function array_to_unique(//This function returns an array of unique values by given array
//Version: 2.0.0.0
$array,
$uniqueCol)
{
$returnArray = array();
$count = count($array);
echo '<br>array count previous unique is: ' .$count;
//Do the if(isset($uniqueCol)) just once - this is more code but faster with long arrays
if(isset($uniqueCol))
{
$helparray = array();
foreach($array as $row)
{
if(!(in_array($row[$uniqueCol],$helparray)))
{
$helparray[] = $row[$uniqueCol];
$returnArray[] = $row;
}
}
}
else{
foreach($array as $row)
{
if(!(in_array($row,$returnArray)))
{$returnArray[] = $row;}
}
}
$count = count($returnArray);
echo '<br>array count after unique is: ' .$count;
return $returnArray;
}
And this is how I call the function for example: 这就是我调用该函数的方式,例如:
array_to_unique($array); //This is okay
array_to_unique($array,'country'); //This is very very slow
Thank you in advance 先感谢您
in_array
has a complexity of O(n)
, meaning it has to go through all elements. in_array
的复杂度为O(n)
,这意味着它必须遍历所有元素。 This is making your code slow. 这使您的代码变慢。
You can optimize the lookup if a value already exists, making use of a hash map instead of searching an array value. 如果值已经存在,则可以优化查找,可以使用哈希映射而不是搜索数组值。 Fortunately, associative arrays in PHP are implemented like that, so we can use the value as key and make a lookup with
array_key_exists
. 幸运的是,PHP中的关联数组是这样实现的,因此我们可以将值用作键并使用
array_key_exists
进行查找。
instead of: 代替:
$helparray = array();
foreach($array as $row)
{
if(!(in_array($row[$uniqueCol],$helparray)))
{
$helparray[] = $row[$uniqueCol];
$returnArray[] = $row;
}
}
take: 采取:
$helparray = array();
foreach($array as $row)
{
if(!(array_key_exists($row[$uniqueCol], $helparray)))
{
$helparray[$row[$uniqueCol]] = true;
$returnArray[] = $row;
}
}
Another thing to consider with very large arrays is that you copy the values to a new array, which increases memory footprint. 对于大型数组,要考虑的另一件事是将值复制到新数组,这会增加内存占用量。 If it is not important for you to that the keys of the return array are 0-indexed continuous integers, you could remove duplicate items from the original array:
如果返回数组的键是0索引的连续整数对您来说并不重要,则可以从原始数组中删除重复的项:
$helparray = array();
foreach($array as $key => $row)
{
if(!(array_key_exists($row[$uniqueCol], $helparray)))
{
$helparray[$row[$uniqueCol]] = true;
}
else
{
unset($array[$key]);
}
}
$deduplicated = [];
foreach ($array as $value) {
$deduplicated[$value['country']] = $value;
}
Simply use the fact that keys are unique and you're automagically deduplicating your array in a single pass. 只需使用键是唯一的事实,就可以在一次通过中自动对数组进行重复数据删除。 If you don't like the new keys, use
array_values()
afterwards. 如果您不喜欢新键,请在以后使用
array_values()
。
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