How to find unique values in two different arrays using isset () and foreach

Question

I want to find unique values in two different arrays. For example, I have $srr1 = [1,3,7,10,13] and $arr2 = [7,4,1,5,3]. I go through arrays

foreach ($arr1 as $key1 => $val1) {
    foreach ($arr2 as $key2 => $val2) {
       if (isset($arr1[$val2]) && $ arr1[$val2] != $val1) {
          echo "$arr1[$val2]"; // here I get 13 3 10 13 10 13 3 10 13 3 3 10, but 3 is superfluous here, because the number 3 is in both the first array and the second array.
       }
    }
}

Can you please tell me how to solve this problem. Thank you in advance.

Answer 1

There are several ways to do it; it just depends on how creative you want to be. This shows three approaches: my preferred method, one that meets you criteria, and lastly a rather not-DRY (don’t repeat yourself) procedural way that I don't recommend.

The first two are nearly identical in the way they work; the first just uses a php built-in function to do it in C. There is not isset() required for the second example; you're just iterating through existing array keys.

Working example at http://sandbox.onlinephpfunctions.com/code/1488860430866c1e5c9428818753cf70b0258f26

<?php

$arr1 = [1,3,7,10,13];
$arr2 = [7,4,1,5,3];

function getUnique(array $a1, array $a2) : array
{
    // initialize output
    $unique = [];
    foreach($a1 as $v) {
        // ignore if present in other array
        if(in_array($v, $a2)) { continue; }
        $unique[] = $v;
    }
    return $unique;
}

print "Example 1\n";
print_r(getUnique($arr1, $arr2));
print_r(getUnique($arr2, $arr1));
print "-----\n\n";


function getUnique2(array $a1, array $a2) : array
{
    // initialize output
    $unique = [];
    foreach($a1 as $v) {

        // for each iteration of outer array, initialize flag as not found
        $foundInArray = false;
        foreach($a2 as $v2) {

            // if you find a match, mark it as so.
            if($v == $v2) {
                $foundInArray = true;

                // (optional) no need to test the rest of the inner array
                break;
            }
        }

        // only store those not marked as found
        if(!$foundInArray) {
            $unique[] = $v;
        }
    }
    return $unique;
}

print "Example 2\n";
print_r(getUnique($arr1, $arr2));
print_r(getUnique($arr2, $arr1));
print "-----\n\n";



// or, a more obscure way
$flip = [];
foreach($arr1 as $v) {
    // increment if we’ve seen this key before
    if(array_key_exists($v, $flip)) {
        $flip[$v]++;
    // initialize if we haven’t 
    } else {
        $flip[$v]=0;
    }
}

// repeat code in a very wet way…
foreach($arr2 as $v) {
    if(array_key_exists($v, $flip)) {
        $flip[$v]++;
    } else {
        $flip[$v]=0;
    }
}

foreach($flip as $k => $v) {
    if($v==0) {
        print "$k\n";
    }
}