What data structure does php have to implement bidirectional index query?

I don’t know how to express it. In short, the requirement is somewhat similar to linq in C#.
Suppose there is the following array

<code>$test = [
    'a'=>'a1',
    'b'=>'a1',
    'c'=>'c1',
]
</code>

I can now query 'a1' through $test['a'], but I also want to query the two elements 'a' and 'b' through 'a1'. How can I implement this in php? ?

Supplement: Some people say to use foreach to implement it, but my array may be very large in the later stage, even as large as thousands or tens of thousands. Using foreach is definitely not efficient.

The existing solutions can only solve the situation where the key value of each array element is different, that is, the one-to-one mapping situation. The first one is array_search, and the second one is array_flip first and then the traditional $test['a1'] search.

Reply content:

I don’t know how to express it. In short, the requirement is somewhat similar to linq in C#.
Suppose there is the following array

<code>$test = [
    'a'=>'a1',
    'b'=>'a1',
    'c'=>'c1',
]
</code>

I can now query 'a1' through $test['a'], but I also want to query the two elements 'a' and 'b' through 'a1'. How can I implement this in php? ?

Supplement: Some people say to use foreach to implement it, but my array may be very large in the later stage, even as large as thousands or tens of thousands. Using foreach is definitely not efficient.

The existing solutions can only solve the situation where the key value of each array element is different, that is, the one-to-one mapping situation. The first one is array_search, and the second one is array_flip first and then the traditional $test['a1'] search.

array_search in the manual can solve your needs.

<code class="php"><?php
$array = array(0 => 'blue', 1 => 'red', 2 => 'green', 3 => 'red');
$key = array_search('green', $array); // $key = 2;
$key = array_search('red', $array);   // $key = 1;
?> </code>

Ask a master in the group to solve the problem, array_keys will be fine.

<code><?php
$a=array("a"=>"Dog","b"=>"Dog","c"=>5,"d"=>"5");
print_r(array_keys($a,"Dog"));
//Array ( [0] => a [1] => b )
 ?>
 </code>

Just enter the code! ~

There is no good way, let’s do it with two arrays

Thank you for the invitation, because the key of the array structure is definitely unique, but different key may correspond to the same value, so as far as I know, if you want to implement c#’s linq, you need to ensure the value of the array The only one,

<code class="php">$test = [
    'a' => 'a1',
    'b' => 'b1',
    'c' => 'c1',
    'd' => 'd1',
    'e' => 'd1'
];

//去除重复的值
$test = array_unique($test);</code>

After removing duplicate values, reverse the array,

<code class="php">$test = [
    'a' => 'a1',
    'b' => 'b1',
    'c' => 'c1',
    'd' => 'd1',
    'e' => 'd1'
];

$test = array_unique($test);

$wocao = array_flip($test);
var_dump($wocao);
</code>

The reverse structure takes the key of the original array as the value, and the value of the original array as the key, as follows

<code>array(4) {
  ["a1"]=> string(1) "a"
  ["b1"]=> string(1) "b"
  ["c1"]=> string(1) "c"
  ["d1"]=> string(1) "d"
}</code>

Now, you can implement linq functions similar to c#

<code>$test = [
    'a' => 'a1',
    'b' => 'b1',
    'c' => 'c1',
    'd' => 'd1',
    'e' => 'd1'
];

$test = array_unique($test);

$wocao = array_flip($test);

$test['a'];   //a1
$wocao['a1']; //a</code>

---

Please point out any shortcomings,,,

Isn’t it just to query the key based on the value? An array_keys can solve it:

<code>$arr = array('a' => 'a1', 'b' => 'a1', 'c' => 'c1');
var_export( array_keys($arr, 'a1') ); //输出键名 a 和 b</code>