Array value matching - return keys - php

Question

I have two arrays. The first one looks like:
Array1
(
[14] => foo
[15] => bar
[16] => hello
}
and the sencond looks like:
Array2
(
[Label1] => foo
[Label2] => bar
[Label3] => hello
[Label4] => foo
[Label5] => bar
}
I would like to compare the values of array1 against array2, if they match, I would like to return the corresponding key of array2.
Any help will be appreciated. Thanks

Answer 1

You can use array_intersect to get the intersection of both arrays:
$arr1 = array(
14=>'foo',
15=>'bar',
16=>'hello'
);
$arr2 = array(
'Label1'=>'foo',
'Label2'=>'bar',
'Label3'=>'hello',
'Label4'=>'foo',
'Label5'=>'bar'
);
var_dump(array_intersect($arr2, $arr1));
This returns:
array(5) {
["Label1"]=>
string(3) "foo"
["Label2"]=>
string(3) "bar"
["Label3"]=>
string(5) "hello"
["Label4"]=>
string(3) "foo"
["Label5"]=>
string(3) "bar"
}
To get the keys of this resulting array, use array_keys. And if you want to get only the first key of each duplicate value, send it through array_unique first:
var_dump(array_keys(array_unique(array_intersect($arr2, $arr1))));
This will get you:
array(3) {
[0]=>
string(6) "Label1"
[1]=>
string(6) "Label2"
[2]=>
string(6) "Label3"
}

Answer 2

You can always use the infamous brute-force "for" iteration:
This gets you all the keys of the values that match. To get just the very first one you would do a simple modification of this code.
PHP Code:
$arr1 = array(
14=>'foo',
15=>'bar',
16=>'hello'
);
$arr2 = array(
'Label1'=>'foo',
'Label2'=>'bar',
'Label3'=>'hello',
'Label4'=>'foo',
'Label5'=>'bar'
);
$results = array();
foreach($arr1 as $val)
foreach($arr2 as $key=>$val2)
if($val == $val2) array_push($results, $key);
// or to get just the first,
// replace the if statement with
//
// if($val == $val2) {
// $result = $key;
// break 2;
// }
print_r($results);
Result is:
array(3) {
[0] => "Label1",
[1] => "Label2",
[2] => "Label3"
}

Answer 3

You can go about like this:
$array1 = array(14 => "foo", 15 => "bar", 16 => "hello");
$array2 = array("Label1" => "foo", "Label2" => "bar", "Label3" => "hello", "Label4" => "foo", "Label5" => "bar", "Label5" => "test");
$result = array_intersect($array2, $array1);
echo '<pre>';
print_r($result);
Output:
Array
(
[Label1] => foo
[Label2] => bar
[Label3] => hello
[Label4] => foo
)
More Info:
array_intersect

Answer 4

You might want to check array_intersect_assoc
<?php
$array1 = array("a" => "green", "b" => "brown", "c" => "blue", "red");
$array2 = array("a" => "green", "yellow", "red");
$result_array = array_intersect_assoc($array1, $array2);
print_r($result_array);
?>
The above example will output:
Array
(
[a] => green
)

Answer 5

A simple loop will be much faster and cleaner than a cascade of built-in functions.
//$arr1, $arr2 as per Gumbo's answer...
$hash = array_flip($arr1);
$keys = array();
foreach($arr2 as $key => $val)
if(isset($hash[$val]))
$keys[] = $key;