Checking if ANY of an array's elements are in another array - php

Question

I have two arrays in PHP as follows:
People:
Array
(
[0] => 3
[1] => 20
)
Wanted Criminals:
Array
(
[0] => 2
[1] => 4
[2] => 8
[3] => 11
[4] => 12
[5] => 13
[6] => 14
[7] => 15
[8] => 16
[9] => 17
[10] => 18
[11] => 19
[12] => 20
)
How do I check if any of the People elements are in the Wanted Criminals array?
In this example, it should return true because 20 is in Wanted Criminals.

Answer 1

You can use array_intersect().
$peopleContainsCriminal = !empty(array_intersect($people, $criminals));

Answer 2

There's little wrong with using array_intersect() and count() (instead of empty).
For example:
$bFound = (count(array_intersect($criminals, $people))) ? true : false;

Answer 3

if 'empty' is not the best choice, what about this:
if (array_intersect($people, $criminals)) {...} //when found
or
if (!array_intersect($people, $criminals)) {...} //when not found

Answer 4

That code is invalid as you can only pass variables into language constructs. empty() is a language construct.
You have to do this in two lines:
$result = array_intersect($people, $criminals);
$result = !empty($result);

Answer 5

Performance test for in_array vs array_intersect:
$a1 = array(2,4,8,11,12,13,14,15,16,17,18,19,20);
$a2 = array(3,20);
$intersect_times = array();
$in_array_times = array();
for($j = 0; $j < 10; $j++)
{
/***** TEST ONE array_intersect *******/
$t = microtime(true);
for($i = 0; $i < 100000; $i++)
{
$x = array_intersect($a1,$a2);
$x = empty($x);
}
$intersect_times[] = microtime(true) - $t;
/***** TEST TWO in_array *******/
$t2 = microtime(true);
for($i = 0; $i < 100000; $i++)
{
$x = false;
foreach($a2 as $v){
if(in_array($v,$a1))
{
$x = true;
break;
}
}
}
$in_array_times[] = microtime(true) - $t2;
}
echo '<hr><br>'.implode('<br>',$intersect_times).'<br>array_intersect avg: '.(array_sum($intersect_times) / count($intersect_times));
echo '<hr><br>'.implode('<br>',$in_array_times).'<br>in_array avg: '.(array_sum($in_array_times) / count($in_array_times));
exit;
Here are the results:
0.26520013809204
0.15600109100342
0.15599989891052
0.15599989891052
0.1560001373291
0.1560001373291
0.15599989891052
0.15599989891052
0.15599989891052
0.1560001373291
array_intersect avg: 0.16692011356354
0.015599966049194
0.031199932098389
0.031200170516968
0.031199932098389
0.031200885772705
0.031199932098389
0.031200170516968
0.031201124191284
0.031199932098389
0.031199932098389
in_array avg: 0.029640197753906
in_array is at least 5 times faster. Note that we "break" as soon as a result is found.

Answer 6

You could also use in_array as follows:
<?php
$found = null;
$people = array(3,20,2);
$criminals = array( 2, 4, 8, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20);
foreach($people as $num) {
if (in_array($num,$criminals)) {
$found[$num] = true;
}
}
var_dump($found);
// array(2) { [20]=> bool(true) [2]=> bool(true) }
While array_intersect is certainly more convenient to use, it turns out that its not really superior in terms of performance. I created this script too:
<?php
$found = null;
$people = array(3,20,2);
$criminals = array( 2, 4, 8, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20);
$fastfind = array_intersect($people,$criminals);
var_dump($fastfind);
// array(2) { [1]=> int(20) [2]=> int(2) }
Then, I ran both snippets respectively at: http://3v4l.org/WGhO7/perf#tabs and http://3v4l.org/g1Hnu/perf#tabs and checked the performance of each. The interesting thing is that the total CPU time, i.e. user time + system time is the same for PHP5.6 and the memory also is the same. The total CPU time under PHP5.4 is less for in_array than array_intersect, albeit marginally so.

Answer 7

Here's a way I am doing it after researching it for a while. I wanted to make a Laravel API endpoint that checks if a field is "in use", so the important information is: 1) which DB table? 2) what DB column? and 3) is there a value in that column that matches the search terms?
Knowing this, we can construct our associative array:
$SEARCHABLE_TABLE_COLUMNS = [
'users' => [ 'email' ],
];
Then, we can set our values that we will check:
$table = 'users';
$column = 'email';
$value = 'alice#bob.com';
Then, we can use array_key_exists() and in_array() with eachother to execute a one, two step combo and then act upon the truthy condition:
// step 1: check if 'users' exists as a key in `$SEARCHABLE_TABLE_COLUMNS`
if (array_key_exists($table, $SEARCHABLE_TABLE_COLUMNS)) {
// step 2: check if 'email' is in the array: $SEARCHABLE_TABLE_COLUMNS[$table]
if (in_array($column, $SEARCHABLE_TABLE_COLUMNS[$table])) {
// if table and column are allowed, return Boolean if value already exists
// this will either return the first matching record or null
$exists = DB::table($table)->where($column, '=', $value)->first();
if ($exists) return response()->json([ 'in_use' => true ], 200);
return response()->json([ 'in_use' => false ], 200);
}
// if $column isn't in $SEARCHABLE_TABLE_COLUMNS[$table],
// then we need to tell the user we can't proceed with their request
return response()->json([ 'error' => 'Illegal column name: '.$column ], 400);
}
// if $table isn't a key in $SEARCHABLE_TABLE_COLUMNS,
// then we need to tell the user we can't proceed with their request
return response()->json([ 'error' => 'Illegal table name: '.$table ], 400);
I apologize for the Laravel-specific PHP code, but I will leave it because I think you can read it as pseudo-code. The important part is the two if statements that are executed synchronously.
array_key_exists() and in_array() are PHP functions.
source:
https://php.net/manual/en/function.array-key-exists.php
https://php.net/manual/en/function.in-array.php
The nice thing about the algorithm that I showed above is that you can make a REST endpoint such as GET /in-use/{table}/{column}/{value} (where table, column, and value are variables).
You could have:
$SEARCHABLE_TABLE_COLUMNS = [
'accounts' => [ 'account_name', 'phone', 'business_email' ],
'users' => [ 'email' ],
];
and then you could make GET requests such as:
GET /in-use/accounts/account_name/Bob's Drywall (you may need to uri encode the last part, but usually not)
GET /in-use/accounts/phone/888-555-1337
GET /in-use/users/email/alice#bob.com
Notice also that no one can do:
GET /in-use/users/password/dogmeat1337 because password is not listed in your list of allowed columns for user.
Good luck on your journey.

Answer 8

I've created a clean Helper Function for you to use.
if (!function_exists('array_has_one')) {
/**
* array_has_one
*
* Uses the search array to match at least one of the haystack to return TRUE
*
* #param {array} $search
* #param {array} $haystack
* #return {boolean}
*/
function array_has_one(array $search, array $haystack){
if(!count(array_intersect($search, $haystack)) === FALSE){
return TRUE;
}else{
return FALSE;
}
}
}
you would use this like
if(array_has_one([1,2,3,4,5], [5,6,7,8,9])){
echo "FOUND 5";
}