How can I loop through two arrays at once? [duplicate]

Question

I am trying to arrange two arrays together and the results keep coming out incorrect. I'll show you my code, the results I'm getting and the results I'm looking for.

I guess I'm just doing it wrong but not sure how else to do it.

My code:

$data1 = [
    'a: 1',
    'a: 2',
    'a: 3',
    'a: 4',
    'a: 5'
];

$data2 = [
    'b: 1',
    'b: 2',
    'b: 3',
    'b: 4',
    'b: 5'
];


foreach($data1 as $item1)
{
    foreach($data2 as $item2)
    {
        echo $item1 . '<br/>';
        echo $item2 . '<br/>';
        echo '<br/><br/>';
    }
}

The Results: (shortened to save space)

a: 1
b: 1

a: 1
b: 2

a: 1
b: 3

a: 1
b: 4

a: 1
b: 5

The results I'm looking for is the following:

a: 1
b: 1

a: 2
b: 2

a: 3
b: 3

a: 4
b: 4

a: 5
b: 5

Answer 1

Problem

Well the problem is of course your nested foreach loop. Because for each element of your $data1 array you loop through the entire $data2 array (So in total there are $data1 * $data2 iterations).

Solutions

To solve this you have to loop through both arrays at once.

array_map() method _{(PHP >=5.3)}

You can do this with array_map() and pass all arrays to it which you want to loop through at the same time.

array_map(function($v1, $v2){
    echo $v1 . "<br>";
    echo $v2 . "<br><br>";
}, $data1, $data2 /* , Add more arrays if needed manually */);

_{Note: If the amount of elements are uneven you won't gen any errors, it will just print NULL (Means you won't see anything)}

MultipleIterator method _{(PHP >=5.3)}

Use a MultipleIterator and attach as many ArrayIterator as you need.

$it = new MultipleIterator();
$it->attachIterator(new ArrayIterator($data1));
$it->attachIterator(new ArrayIterator($data2));
//Add more arrays if needed 

foreach($it as $a) {
    echo $a[0] . "<br>";
    echo $a[1] . "<br><br>";
}

_{Note: If the amount of elements are uneven it will just print all values where both arrays still have values}

for loop method _{(PHP >=4.3)}

Use a for loop with a counter variable, which you can use as key for both arrays.

$keysOne = array_keys($data1);
$keysTwo = array_keys($data2);

$min = min(count($data1), count($data2));

for($i = 0; $i < $min; $i++) {
    echo $data1[$keysOne[$i]] . "<br>";
    echo $data2[$keysTwo[$i]] . "<br><br>";
}

_{Note: Using array_keys() is just so that this also works if the arrays don't have the same keys or are associative. min() is used to only loop through as many elements as every array has}

array_combine() method _{(PHP >=5.0)}

Or if the arrays only have unique values, you can array_combine() both arrays, so that $data1 can be accessed as key and $data2 as value.

foreach(array_combine($data1, $data2) as $d1 => $d2) {
    echo $d1 . "<br>";
    echo $d2 . "<br><br>";
}

_{Note: The arrays must have the same amount of elements, otherwise array_combine() will throw an error}

call_user_func_array() method _{(PHP >=5.6)}

If you want to print more than 2 arrays at the same time or just an unknown amount of arrays, you can combine the array_map() method with a call_user_func_array() call.

$func = function(...$numbers){
    foreach($numbers as $v)
        echo $v . "<br>";
    echo "<br>";
};
call_user_func_array("array_map", [$func, $data1, $data2]);

_{Note: Since this kinda uses the array_map() method, it behaves the same with uneven amount of elements. Also since this method only works for PHP >=5.6 you can just remove the arguments and change out $numbers with func_get_args() in the foreach loop and then it also works for PHP >=5.3}