Say i start with a simple array (which could be theoretically of any length):
$ids = array(1,2,3,4);
What it the best solution for splitting this array into an array of unique pairs like:
$pair[0] = array(1,2);
$pair[1] = array(1,3);
$pair[2] = array(1,4);
$pair[3] = array(2,3);
$pair[4] = array(2,4);
$pair[5] = array(3,4);
The simplest solution is to use a nested loop and build combinations as you go, although note that the complexity here is O(n2).
$ids = array(1,2,3,4,4);
$combinations = array();
$ids = array_unique($ids); // remove duplicates
$num_ids = count($ids);
for ($i = 0; $i < $num_ids; $i++)
{
for ($j = $i+1; $j < $num_ids; $j++)
{
$combinations[] = array($ids[$i], $ids[$j]);
}
}
See this in action at http://www.ideone.com/9wzvP
in_array check by doing array_unique on $ids. And you can also speed it up by counting $ids as a precondition before the loops (since it's not going to change). I only mention these since you do mention the complexity...
$ids first, though that won't affect the complexity. I don't think you can use array_unique ahead of time though... it depends on the OP's goal. ie. if $ids = array(1,2,3,3), should [3,3] be a result?
$ids won't affect complexity significantly (since it's an O(1) function), but in_array is not O(1) (I'm not positive, but I think it may be O(n), but I may be mistaken), so that would affect complexity. And yes, it does depend on the goal (The OP is not asking for a true cartesian product, but a limited one (and I can't remember the name for it off the top of my head))...array_unique is probably O(n^2) as well, no? (See stackoverflow.com/questions/478002/…)Probably not the best solution
$ids = array(1,2,3,4);
$pairs = array();
foreach($ids as $key => $data){
foreach($ids as $subkey => $subdata){
if( $subkey != $key){
if(!in_array(array($subdata, $data) , $pairs) ){
$pairs[] = array($data, $subdata);
}
}
}
}
Anyway it works
Fixed from my initial jump-the-gun suggestion of array_chunk()
Try this instead:
$ids = array(1, 2, 3, 4);
$out = array();
while ($item = array_shift($ids)) {
foreach ($ids as $key=>$value) {
$out[] = array($item, $value);
}
}
array_chunk won't do what the OP wants, look at the example output. OP wants combinations.Sweet solution, Nev Stokes! I changed the 'while' statement to avoid the loop from breaking when one of the values is 0:
$ids = array(0, 1, 2, 3, 4);
$out = array();
while ( !is_null( $item = array_shift($ids) ) ) {
foreach ($ids as $key=>$value) {
$out[] = array($item, $value);
}
}
$ids = array(1,2,3,4);
$result=array();
foreach($ids as $value_1)
{
foreach($ids as $value_2)
{
if($value_1 !=$value_2)
{
$result[]=array($value_1,$value_2);
}
}
}
echo "<pre>";
print_r($result);
$pair = array_chunk($ids, 2);
