Check Whether an Array is Subset of Another Array in PHP

Given two arrays i.e. subset and superset, the task is to check whether an array is subset of another array in PHP. This article covers various methods to determine whether an array is a subset of another array.

These are the following approaches:

Using array_diff() Function

The array_diff() function computes the difference of arrays. If the result of the difference between the subset array and the superset array is empty, it means all elements of the subset are present in the superset.

• array_diff($subset, $superset) returns an array containing elements in $subset that are not in $superset.
• If this difference is empty, $subset is a subset of $superset.

Example: This example shows the checking of if an array is a subset of another array using array_diff() function.

<?php

function isSubset($subset, $superset) {
    return empty(array_diff($subset, $superset));
}

// Driver code
$subset = [1, 2, 3];
$superset = [1, 2, 3, 4, 5];

if (isSubset($subset, $superset)) {
    echo "Array is a subset";
} else {
    echo "Array is not a subset";
}

?>

Array is a subset

Using array_intersect() Function

The array_intersect() function returns an array of values that are present in all the input arrays. If the intersection of the subset array and the superset array has the same number of elements as the subset array, then the subset is entirely contained within the superset.

• array_intersect($subset, $superset) returns an array containing elements found in both $subset and $superset.
• If the count of this intersection equals the count of $subset, then $subset is a subset of $superset.

Example: This example shows the checking of if an array is a subset of another array using array_intersect() function.

<?php

function isSubset($subset, $superset) {
    return count(array_intersect($subset, $superset)) == count($subset);
}

// Driver code
$subset = [1, 2, 3];
$superset = [1, 2, 3, 4, 5];

if (isSubset($subset, $superset)) {
    echo "Array is a subset";
} else {
    echo "Array is not a subset";
}

?>

Array is a subset

Using Loops and in_array() Function

A more manual approach involves looping through each element in the subset array and checking if it exists in the superset array using in_array() function.

• Iterate through each element in $subset.
• Use in_array() function to check if the element is in $superset.
• If any element is not found, return false. If all elements are found, return true.

Example: This example shows the checking of if an array is a subset of another array using lops and in_array_diff() function.

<?php

function isSubset($subset, $superset) {
    foreach ($subset as $element) {
        if (!in_array($element, $superset)) {
            return false;
        }
    }
    return true;
}

// Driver code
$subset = [1, 2, 3];
$superset = [1, 2, 3, 4, 5];

if (isSubset($subset, $superset)) {
    echo "Array is a subset";
} else {
    echo "Array is not a subset";
}

?>

Array is a subset

Using array_flip() and array_key_exists() Functions

The array_flip() function flips the keys and values of an array. By flipping the superset array and then checking if each element in the subset array exists as a key in the flipped superset array using array_key_exists(), we can determine if the subset is contained within the superset.

Steps:

1. Flip the superset array using array_flip().
2. Iterate through each element in the subset array.
3. Use array_key_exists() to check if the element exists in the flipped superset array.
4. If any element is not found, return false. If all elements are found, return true.

Example: This example shows the checking of if an array is a subset of another array using array_flip() and array_key_exists() functions.

<?php

function isSubset($subset, $superset) {
    $flippedSuperset = array_flip($superset);
    foreach ($subset as $element) {
        if (!array_key_exists($element, $flippedSuperset)) {
            return false;
        }
    }
    return true;
}

$subset = [1, 2, 3];
$superset = [1, 2, 3, 4, 5];

if (isSubset($subset, $superset)) {
    echo "Array is a subset";
} else {
    echo "Array is not a subset";
}

?>

Output
Array is a subset

Array is a subset
Output
Array is a subset