Cluster PHP array - php

Question

Let's say I have an array of items with each item a value. I'd like to
create a new array where the items are clustered by their relative distance to each other.
When an item has a distance of one to another item, they belong to each other.
$input = [
'item-a' => 1,
'item-b' => 2,
'item-c' => 3,
'item-d' => 5,
];
$output = [
['item-a', 'item-b'],
['item-b', 'item-c'],
['item-d'],
];
This will create an output of overlapping arrays. What I want is that, because item-a and item-b are related, and item-b is also
related to item-c, I'd like to group item-a, item-b, and item-c to each other. The distance to item-c and item-d is greater than
1 so it will for a cluster of itself.
$output = [
['item-a', 'item-b', 'item-c'],
['item-d'],
];
How do I even start coding this?
Thanks in advance and have a nice day!

Answer 1

This can only be tested in your environment but here is what it does
it attempts to find relative distances based on array index 0's hash
it resorts the input array by distances (assuming that in this stage some will be positive and some negative) - that gives us the info to put the hash array in an order
Take this new array and put the hash back in
build a final output array measuring distances and sorting the level of output array by a threshhold.
I put in a couple dummy functions to return distances, obviously replace with your own. This might need tweaking but at this point, it's in your hands.
<?php
// example code
$input = [
'item-a' => 'a234234d',
'item-f' => 'h234234e',
'item-h' => 'e234234f',
'item-b' => 'f234234g',
'item-m' => 'd234234j',
'item-d' => 'm234234s',
'item-e' => 'n234234d',
'item-r' => 's234234g',
'item-g' => 'f234234f',
];
function getDistanceFrom($from, $to) {
return rand(-3,3);
}
function getDistanceFrom2($from, $to) {
return rand(0,7);
}
// first sort by relative distance from the first one
$tmp = [];
$ctr = 0;
foreach ($input as $item => $hash) {
if ($ctr === 0) { $ctr ++; continue; }
$tmp[$item]=getDistanceFrom(reset($input), $hash);
}
uasort($tmp, function ($a, $b)
{
return ($a < $b) ? -1 : 1;
});
//now they're in order, ditch the relative distance and put the hash back in
$sortedinput = [];
foreach ($tmp as $item => $d) {
$sortedinput[$item] = $input[$item];
}
$output=[];
$last=0;
$level=0;
$thresh = 3; // if item is within 3 of the previous, group
foreach($sortedinput as $v=>$i) {
$distance = getDistanceFrom2($last, $i);
if (abs($distance) > $thresh) $level++;
$output[$level][]=array("item" => $v, "distance" => $distance, "hash" => $i);
$last = $i;
}
print_r($output);