# php - Filter 2D associative array using keys from multiple levels of another 2D associative array

16

I have two 2-dimensional arrays and want to filter the first array's data using the second array so that the only elements retained are where the keys in the first and second levels match.

``````\$array1 = [
'a1' => ['a_name' => 'aaaaa', 'a_value' => 'aaa'],
'b1' => ['b_name' => 'bbbbb', 'b_value' => 'bbb'],
'c1' => ['c_name' => 'ccccc', 'c_value' => 'ccc'],
];

\$array2 = [
'b1' => ['b_name' => 'does not matter'],
];
``````

In other words, I want the intersection of keys of`\$array1` and`\$array2`. The result must be from`\$array1`.

Desired result:

``````['b1' => ['b_name' => 'bbbbb']]
``````
970

### Answer

#### Solution:

``````function recursive_array_intersect_key(array \$array1, array \$array2) {
\$array1 = array_intersect_key(\$array1, \$array2);
foreach (\$array1 as \$key => &\$value) {
if (is_array(\$value) && is_array(\$array2[\$key])) {
\$value = recursive_array_intersect_key(\$value, \$array2[\$key]);
}
}
return \$array1;
}
``````

Demo here.

274

### Answer

#### Solution:

``````\$output = array_intersect_key(\$array1, \$array2);
``````
161

## Demo of 2 dimensional associative array intersection in PHP

The Code:

``````<?php
function compare_states(\$a1, \$a2){
\$diff1 = strcasecmp(\$a1['state_id'], \$a2['state_id']);
\$diff2 = strcasecmp(\$a1['state_name'], \$a2['state_name']);
if (\$diff1 != 0) return \$diff1;
if (\$diff2 != 0) return \$diff2;
return 0;
}
function calculate_intersection(\$a1, \$a2){
return array_uintersect(\$a1, \$a2, 'compare_states');
}
?>
``````

How to run it:

``````<?php
\$a = Array(Array("state_id"=>14, "state_name"=>"Illinois"));
\$b = Array(Array("state_id"=>14, "state_name"=>"Illinois"));
\$new = calculate_intersection(\$a, \$b);
print_r(\$a);
//in this simple case, the intersection is equivalent to \$a.
\$a = Array(Array("state_id"=>14, "state_name"=>"Illinois"));
\$b = Array(Array("state_id"=>14, "state_name"=>"Foobar"));
\$new = calculate_intersection(\$a, \$b);
print_r(\$a);
//in this case, the intersection is empty.
?>
``````

Unit tests to prove that the above code works as designed:

``````\$a = Array();
\$b = Array();
\$new = calculate_intersection(\$a, \$b);
print "\nGroup1\n";
print ((count(\$new) == count(\$a) && count(\$a) == count(\$b)) ? "." : "FAIL");
print ((count(\$new) == 0) ? "." : "FAIL");
//==============================================
\$a = Array(Array("state_id"=>14, "state_name"=>"Illinois"));
\$b = Array(Array("state_id"=>14, "state_name"=>"Illinois"));
\$new = calculate_intersection(\$a, \$b);
print "\nGroup2\n";
print ((count(\$new) == count(\$a) && count(\$a) == count(\$b)) ? "." : "FAIL");
print ((count(\$new) == 1) ? "." : "FAIL");
print ((\$new[0]['state_id'] == 14 ? "." : "FAIL"));
print ((\$new[0]['state_name'] == "Illinois" ? "." : "FAIL"));
//==============================================
print "\nGroup3\n";
\$a = Array(Array("state_id"=>14, "state_name"=>"Illinois"), Array("state_id"=> "22", "state_name"=>"Massachusetts"));
\$b = Array(Array("state_id"=>14, "state_name"=>"Illinois"), Array("state_id"=> "22", "state_name"=>"Massachusetts"));
\$new = calculate_intersection(\$a, \$b);
print ((count(\$new) == count(\$a) && count(\$a) == count(\$b)) ? "." : "FAIL");
print ((\$new[0]['state_id'] == 14 ? "." : "FAIL"));
print ((\$new[0]['state_name'] == "Illinois" ? "." : "FAIL"));
print ((\$new[1]['state_id'] == 22 ? "." : "FAIL"));
print ((\$new[1]['state_name'] == "Massachusetts" ? "." : "FAIL"));
//==============================================
\$a = Array(Array("state_id"=>"14", "state_name"=>"Illinois"));
\$b = Array(Array("state_id"=>"22", "state_name"=>"Massachusetts"));
\$new = calculate_intersection(\$a, \$b);
print "\nGroup5\n";
print ((count(\$new) == 0) ? "." : "FAIL");
//==============================================
\$a = Array(Array("state_id"=>"14", "state_name"=>"Illinois"));
\$b = Array(Array("state_id"=>"14", "state_name"=>"Illinois"), Array("state_id"=>"22", "state_name"=>"Massachusetts"));
\$new = calculate_intersection(\$a, \$b);
print "\nGroup6\n";
print ((count(\$new) == 1) ? "." : "FAIL");
print ((\$new[0]['state_id'] == 14) ? "." : "FAIL");
print ((\$new[0]['state_name'] == "Illinois") ? "." : "FAIL");
//==============================================
\$a = Array(Array("state_id"=>"14", "state_name"=>"Illinois"));
\$b = Array(Array("state_id"=>"22", "state_name"=>"Massachusetts"), Array("state_id"=>"14", "state_name"=>"Illinois"));
\$new = calculate_intersection(\$a, \$b);
print "\nGroup7\n";
print ((count(\$new) == 1) ? "." : "FAIL");
print ((\$new[0]['state_id'] == 14) ? "." : "FAIL");
print ((\$new[0]['state_name'] == "Illinois") ? "." : "FAIL");
//==============================================
\$a = Array(Array("state_id"=>"14", "state_name"=>"Illinois"));
\$b = Array(Array("state_id"=>"22", "state_name"=>"Massachusetts"), Array("state_id"=>"14", "state_name"=>"Fromulate"));
\$new = calculate_intersection(\$a, \$b);
print "\nGroup8\n";
print ((count(\$new) == 0) ? "." : "FAIL");
//==============================================
\$a = Array(Array("state_id"=>"14", "state_name"=>"Illinois"), Array("state_id"=>"14", "state_name"=>"Illinois"));
\$b = Array(Array("state_id"=>"14", "state_name"=>"Illinois"), Array("state_id"=>"14", "state_name"=>"Illinois"));
\$new = calculate_intersection(\$a, \$b);
print "\nGroup9\n";
print ((count(\$new) == 2) ? "." : "FAIL");
print ((\$new[0]['state_id'] == 14) ? "." : "FAIL");
print ((\$new[0]['state_name'] == "Illinois") ? "." : "FAIL");
print ((\$new[1]['state_id'] == 14) ? "." : "FAIL");
print ((\$new[1]['state_name'] == "Illinois") ? "." : "FAIL");
//==============================================
\$a = Array(Array("state_id"=>"14", "state_name"=>"Illinois"), Array("state_id"=>"22", "state_name"=>"Massachusetts"));
\$b = Array(Array("state_id"=>"22", "state_name"=>"Massachusetts"), Array("state_id"=>"14", "state_name"=>"Illinois"));
\$new = calculate_intersection(\$a, \$b);
print "\nGroup7\n";
print ((count(\$new) == 2) ? "." : "FAIL");
print ((\$new[0]['state_id'] == 14) ? "." : "FAIL");
print ((\$new[0]['state_name'] == "Illinois") ? "." : "FAIL");
print ((\$new[1]['state_id'] == 22) ? "." : "FAIL");
print ((\$new[1]['state_name'] == "Massachusetts") ? "." : "FAIL");
?>
``````

The above code prints:

``````[email protected] \$ php a.php
Group1
..
Group2
....
Group3
.....
Group5
.
Group6
...
Group7
...
Group8
.
Group9
.....
Group7
.....
``````

All dots means everything passed.

What cases does this code take care of?

1. Both arrays being empty. Intersection is empty.
2. One empty and the other with items. Intersection is empty.
3. Both arrays have identical items, set: 1 and set: n. Intersection is equivalent to the first array.
4. Both arrays are identical, except shuffled. Intersection is equivalent to first array.
5. The arrays are identical except the state_name is different in each case, and the state_id is the same. Intersection is empty.
6. Array a has items uncommon to b, items common to B. Array b has items uncommon to a and items common to A. Intersection is the items common to both a and b.

What it doesn't do:

It doesn't test for nulls/undefined/dissimilar depth arrays, nor arrays 2 or more layers deep. If datatypes get swapped, comparing strings to ints, or floats to octals, it will probably fail. It's difficult to get PHP to do equality correctly. http://eev.ee/blog/2012/04/09/php-a-fractal-of-bad-design/

Do everything you can to try to do this work in the database, doing it in PHP blows the horn to summon the fail whale. It's inefficient, so you better not be operating on more than a few hundred items. It's going to surprise left jab you on unexpected cases, and it's kind of hard to read/understand what it's doing under the hood.

194

### Answer

#### Solution:

Because you are filtering arrays of consistent depth, recursion is not explicitly required.

• Filter on the first level keys with`array_intersect_key()`.
• Then filter each related row (the second level elements) between the two arrays.
• If there are no intersections in a given row, remove the first level key as well -- because the requirement of this question is to only keep the data that matches the first AND second level keys.

Code: (Demo)

``````\$array1 = [
'a1' => ['a_name' => 'aaaaa', 'a_value' => 'aaa'],
'b1' => ['b_name' => 'bbbbb', 'b_value' => 'bbb'],
'c1' => ['c_name' => 'ccccc', 'c_value' => 'ccc'],
];

\$array2 = [
'b1' => ['b_name' => 'bbbbb'],
'c1' => ['a_value' => 'aaa']
];

\$result = array_intersect_key(\$array1, \$array2);
foreach (\$result as \$key => &\$value) {
\$value = array_intersect_key(\$value, \$array2[\$key]);
if (!\$value) {
unset(\$result[\$key]);
}
}
var_export(\$result);
``````

Output:

``````array (
'b1' =>
array (
'b_name' => 'bbbbb',
),
)
``````
445

### Answer

#### Solution:

I think you should check if the \$array2[\$key] is an array, too.

``````function recursive_array_intersect_key(array \$array1, array \$array2) {
\$array1 = array_intersect_key(\$array1, \$array2);
foreach (\$array1 as \$key => &\$value) {
if (is_array(\$value) && is_array(\$array2[\$key])) {
\$value = recursive_array_intersect_key(\$value, \$array2[\$key]);
}
}
return \$array1;
}
``````

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