How do I make pairs of array values? - php

Question

Consider the following array as input:
$input = array('A', 'B', 'C', 'D');
I'm looking for a way to make loop though this array, writing down every possible pair of two values. In this example: AB AC AD BC BD CD. Please not that BA doesn't count as a pair, since AB is already mentioned:
$output = array(
'A' => 'B',
'A' => 'C',
'A' => 'D',
'B' => 'C',
'B' => 'D'
);
Any input on how to get this started is appreciated!

Answer 1

$output=array();
for ($i=0;$i<sizeof($input);$i++) {
$k=$input[$i];
for ($j=$i+1;$j<sizeof($input);$j++) {
$v=$input[$j];
$output[]=array($k=>$v);
}
}
Edit
As of your comment, the restructured output
$output=array();
//See below
for ($i=0;$i<sizeof($input);$i++) {
$k=$input[$i];
$v=array();
for ($j=$i+1;$j<sizeof($input);$j++) {
$v[]=$input[$j];
}
$output[]=array($k=>$v);
}
This will give you 'D'=>Array() as a last row, if you don't want hti you have to change
for ($i=0;$i<sizeof($input);$i++) {
to
for ($i=0;$i<sizeof($input)-1;$i++) {

Answer 2

something like this maybe;
$input = array('A', 'B', 'C', 'D');
$input_copy = $input;
$output = array();
$i = 0;
foreach($input as $val) {
$j = 0;
foreach($input_copy as $cval) {
if($j < $i) break;
$output[] = array($val => $cval);
$j++;
}
$i++;
}
$output = array(
0 => array('A' => 'A'),
1 => array('A' => 'B'),
2 => array('A' => 'C'),
...
);
Note that your output array is impossible, as the key is overwritten each time

Answer 3

This won't be possible in PHP, as PHP array can have only unique keys.
You can get output as
$output = array(
'A' => array('B','C','D'),
'B' => array('C','D')
);
$input = array('A', 'B', 'C', 'D');
foreach($input as $key => $value){
$tempKey = $key;
for($key +1 ; $key < count($input) ; $key++){
$result[$tempKey][] = $input[$key];
}
}

Answer 4

You can use this generic method:
function combine($inputArray, &$outputArray, $index, $combLen) {
global $outstr;
for ($i = $index; $i < count($inputArray); $i++) {
$outstr.=$inputArray[$i];
if(strlen($outstr) == $combLen) {
$outputArray[]= $outstr;
}
combine($inputArray, $outputArray, $i + 1, $combLen);
$outstr = substr($outstr, 0, strlen($outstr)-1);
}
}
See it on ideone

Answer 5

if you need to work with pairs as arrays
$pairs = [];
foreach($a as $k => $v) {
foreach(array_slice($a, $k + 1) as $k2 => $v2) {
$pairs[] = [$v, $v2];
}
}