PHP - How do you find duplicate value groupings in an array

Question

I have an array of string values which sometimes form repeating value patterns ('a', 'b', 'c', 'd')

$array = array(
    'a', 'b', 'c', 'd',
    'a', 'b', 'c', 'd',
    'c', 'd',
);

I would like to find duplicate patterns based on the array order and group them by that same order (to maintain it).

$patterns = array(
    array('number' => 2, 'values' => array('a', 'b', 'c', 'd')),
    array('number' => 1, 'values' => array('c'))
    array('number' => 1, 'values' => array('d'))
);

Notice that [a,b], [b,c], & [c,d] are not patterns by themselves because they are inside the larger [a,b,c,d] pattern and the last [c,d] set only appears once so it's not a pattern either - just the individual values 'c' and 'd'

Another example:

$array = array(
    'x', 'x', 'y', 'x', 'b', 'x', 'b', 'a'
  //[.......] [.] [[......]  [......]] [.]
);

which produces

$patterns = array(
    array('number' => 2, 'values' => array('x')),
    array('number' => 1, 'values' => array('y')),
    array('number' => 2, 'values' => array('x', 'b')),
    array('number' => 1, 'values' => array('a'))
);

How can I do this?

Answer 1

Character arrays are just strings. Regex is the king of string pattern matching. Add recursion and the solution is pretty elegant, even with the conversion back and forth from character arrays:

function findPattern($str){
    $results = array();
    if(is_array($str)){
        $str = implode($str);
    }
    if(strlen($str) == 0){ //reached the end
        return $results;
    }
    if(preg_match_all('/^(.+)\1+(.*?)$/',$str,$matches)){ //pattern found
        $results[] = array('number' => (strlen($str) - strlen($matches[2][0])) / strlen($matches[1][0]), 'values' => str_split($matches[1][0]));
        return array_merge($results,findPattern($matches[2][0]));
    }
    //no pattern found
    $results[] = array('number' => 1, 'values' => array(substr($str, 0, 1)));
    return array_merge($results,findPattern(substr($str, 1)));
}

You can test here : https://eval.in/507818 and https://eval.in/507815

Answer 2

If c and d can be grouped, this is my code:

<?php
$array = array(
    'a', 'b', 'c', 'd',
    'a', 'b', 'c', 'd',
    'c', 'd',
);

$res = array();

foreach ($array AS $value) {
    if (!isset($res[$value])) {
        $res[$value] = 0;
    }
    $res[$value]++;
}

foreach ($res AS $key => $value) {
    $fArray[$value][] = $key;
    for ($i = $value - 1; $i > 0; $i--) {
        $fArray[$i][] = $key;
    }
}

$res = array();
foreach($fArray AS $key => $value) {
    if (!isset($res[serialize($value)])) {
        $res[serialize($value)] = 0;
    }
    $res[serialize($value)]++;
}
$fArray = array();
foreach($res AS $key => $value) {
    $fArray[] = array('number' => $value, 'values' => unserialize($key));
}

echo '<pre>';
var_dump($fArray);
echo '</pre>';

Final result is:

array (size=2)
  0 => 
    array (size=2)
      'number' => int 2
      'values' => 
        array (size=4)
          0 => string 'a' (length=1)
          1 => string 'b' (length=1)
          2 => string 'c' (length=1)
          3 => string 'd' (length=1)
  1 => 
    array (size=2)
      'number' => int 1
      'values' => 
        array (size=2)
          0 => string 'c' (length=1)
          1 => string 'd' (length=1)