Futz testing arsort() dependent code? - php

Question

It seems that a large, complicated codebase depends on the order arsort produces. Before I dive in to discern what's actually happening in like 50 classes -- is there a simple way to shuffle items with equal values?
In other words, if the input is
['foo' => 3, 'bar' => 3, 'baz' => 3, 'this' => 2, 'that' => 2]
I'd like to get
['baz' => 3, 'bar' => 3, 'foo' => 3, 'this' => 2, 'that' => 2]
one run maybe, then
['baz' => 3, 'bar' => 3, 'foo' => 3, 'that' => 2, 'this' => 2]
on another random run.

Answer 1

How about something like this? (Untested)
Worst Case complexity: O(k)
Note: Written for algorithmic clarity and not PHP details...
function shuffleInput( $data ) {
// Separate into sets.
$sets = [];
foreach ( $data as $k => $v ) {
$sets[$v][] = $k;
}
// Shuffle & Join.
$data = [];
foreach ( $sets as $v => &$set ) {
shuffle( $set );
foreach( $set as $k ) {
$data[$k] = $v;
}
}
return $data;
}
Depending on the size of your input, it might be a better idea to unset every element in $data in the first loop instead of just creating a new array. This applies if data is very large and memory is precious to you - as well as reducing any sudden spikes & dips in memory usage.
Also, if you're going to continously shuffle the same $data around you might want to separate out the making of $sets to some other place or at least allow the developer to pass/get it as a side effect.

Answer 2

If you do not want to deal with shuffle, but rather prefer to check all permutations of the array, then you can do something like this:
$arr = array('foo' => 3, 'bar' => 3, 'baz' => 3, 'this' => 2, 'that' => 2);
$keys = array_keys($arr);
$indexes = range(0, count($arr) - 1);
pc_permute($indexes, $perms);
var_dump($perms);
function pc_permute($items, &$ret = array(), $perms = array( )) {
if (empty($items)) {
$ret[] = $perms;
} else {
for ($i = count($items) - 1; $i >= 0; --$i) {
$newitems = $items;
$newperms = $perms;
list($foo) = array_splice($newitems, $i, 1);
array_unshift($newperms, $foo);
pc_permute($newitems, $ret, $newperms);
}
}
}
Array $perms will give all permutations of the indexes, key name by index you can get from $keys and value by key or index (use array_slice) from $arr :)
ps: but you should understand - more elements you have in the original array, more permutations you will find. if there are n elements then there will be n! permutations. for n = 5 there are 120 permutations.