Even distribution of PHP arrays across columns - php

Question

So, I want to distribute evenly lists across 3 columns. The lists cannot be broken up or reordered.
At the moment, I have 5 lists each containing respectively 4, 4, 6, 3 and 3 items.
My initial approach was:
$lists = [4,4,6,3,3];
$columns = 3;
$total_links = 20;
$items_per_column = ceil($total_links/$columns);
$current_column = 1;
$counter = 0;
$lists_by_column = [];
foreach ($lists as $total_items) {
$counter += $total_items;
$lists_by_column[$current_column][] = $total_items;
if ($counter > $current_column*$links_per_column) {
$current_column++;
}
}
Results in:
[
[4],
[4,6],
[3,3]
]
But, I want it to look like this:
[
[4,4],
[6],
[3,3]
]
I want to always have the least possible variation in length between the columns.
Other examples of expected results:
[6,4,4,6] => [[6], [4,4], [6]]
[4,4,4,4,6] => [[4,4], [4,4], [6]]
[10,4,4,3,5] => [[10], [4,4], [3,5]]
[2,2,4,6,4,3,3,3] => [[2,2,4], [6,4], [3,3,3]]

Answer 1

Roughly what you need to do is loop over the number of columns within your foreach(). That will distribute them for you.
$numrows = ceil(count($lists) / $columns);
$thisrow = 1;
foreach ($lists as $total_items) {
if($thisrow < $numrows){
for($i = 1; $i <= $columns; $i++){
$lists_by_column[$i][] = $total_items;
}
}else{
//this is the last row
//find out how many columns need to fit.
//1 column is easy, it goes in the first column
//2 columns is when you'll need to skip the middle one
//3 columns is easy because it's full
}
$thisrow++;
}
This will be an even distribution, from left to right. But you actually want a modified even distribution that will look symmetrical to the eye. So within the foreach loop, you'll need to keep track of 1.) if you're on the last row of three, and 2.) if there are 2 remainders, to have it skip col2 and push to col3 instead. You'll need to set that up to be able to play around with it,...but you're just a couple of logic gates away from the land of milk and honey.

Answer 2

So, I ended up using this code:
$lists = [4,4,6,3,3];
$columns = 3;
$total_links = 20;
$items_per_column = ceil($total_links/$columns);
$current_column = 1;
$lists_by_column = [];
for ($i = 0; $i < count($lists); $i++) {
$total = $lists[$i];
$lists_by_column[$current_column][] = $lists[$i];
//Loop until reaching the end of the column
while ($total < $items_per_column && $i+1 < count($lists)) {
if ($total + $lists[$i+1] > $items_per_column) {
break;
}
$i++;
$total += $lists[$i];
$lists_by_column[$current_column][] = $lists[$i];
}
//When exiting the loop the last time we need another break
if (!isset($lists[$i+1])) {break;}
//If the last item goes onto the next column
if (abs($total - $items_per_column) < abs($total + $lists[$i+1] - $items_per_column)) {
$current_column++;
//If the last item goes onto the current column
} else if ($total + $lists[$i+1] > $items_per_column) {
$i++;
$lists_by_column[$current_column][] = $lists[$i];
$current_column++;
}
}