Group items by 3 in for each loop - php

Question

I have an array of items and want to loop through them but instead of grouping them inside of a div I would like to group them by css Class.
I dont want to do div grouping because of mobile views there might be 4 or more in line and the breaks css class will change as the screen size changes or will be moved to absolute positioning removing the break all together and forming a grid.
I can create the breaks every 3 items but the class assign im struggling with.
Any help would be appreciated.
I would like to create the below layout in a PHP foreach loop.
ex.
<div class="listing">
<div class="group_1">item1</div>
<div class="group_1">item2</div>
<div class="group_1">item3</div>
<div class="break_1"></div>
<div class="group_2">item4</div>
<div class="group_2">item5</div>
<div class="group_2">item6</div>
<div class="break_2"></div>
<div class="group_3">item7</div>
<div class="group_3">item8</div>
<div class="group_3">item9</div>
<div class="break_3"></div>
<div class="group_4">item10</div>
<div class="group_4">item11</div>
<div class="group_4">item12</div>
<div class="break_4"></div>
</div>

Answer 1

Not very sure if it is what you are looking, anyway, given a basic array like this:
$arr=array(1,2,3,4,5,6,7,8,9,10,11,12);
you can loop it and have the code you expect this way:
$group_num=1;
echo "<div class='listing'>";
foreach ($arr as $key=>$item) {
echo "<div class='group_$group_num'>$item</div>";
if ($key%3==0) {
echo "<div class='break'></div>";
$group_num++;
}
}
echo "</div>";
Results:
<div class='listing'>
<div class='group_1'>1</div>
<div class='group_1'>2</div>
<div class='group_1'>3</div>
<div class='break'></div>
<div class='group_2'>4</div>
<div class='group_2'>5</div>
<div class='group_2'>6</div>
<div class='break'></div>
<div class='group_3'>7</div>
<div class='group_3'>8</div>
<div class='group_3'>9</div>
<div class='break'></div>
<div class='group_4'>10</div>
<div class='group_4'>11</div>
<div class='group_4'>12</div>
<div class='break'></div>

Answer 2

if we have array of items as :
$items = ['item1', 'item2', 'item3', 'item4', 'item5', 'item6', 'item7', 'item8'];
$result = '';
foreach($items as $index => $item) {
$groupNumber = intval(floor($index/3)) + 1;
$result .= "<div class='group_$groupNumber'>$item</div>";
}
echo $result;
and this is a sample output

Answer 3

Thanks to the help of Giacomo Pittalis and Hassan Ali Salem I have managed to solve this in a bit of a crude way.
<?php
$items = ['item1', 'item2', 'item3', 'item4', 'item5', 'item6', 'item7', 'item8', 'item9', 'item10'];
$i = 0;
$len = count($items);
foreach ($items as $item) {
$mod = intval(floor($i / 3) + 1);
echo '<div class="' . 'group_' . $mod . '">' . $items[$i] . '</div>';
if (($i % 3 == 2)) { ?>
<div class="content_holder hidden" id="group_<?php echo $mod; ?>"></div>
<?php }
if ($i == $len - 1) { ?>
<div class="content_holder hidden" id="group_<?php echo $mod; ?>"></div>
<?php }
$i++;
}
?>