Create described structure from the given string (name of software can't be repeated even though years/versions can)

StringtoArray.php

<?php

// Given String:
$string = "word_2007, word_2010, word_2007, sublime, phpstorm_2010, phpstorm_2010, 
           netbeans, netbeans, sublime, word_2007, phpstorm_2010, atom";

// Desired Structure:
//  sample : ['word' => [2007, 2010], 'sublime', 'netbeans', 'phpstorm' => [2010], 'atom'];

/* 1. Solution
 What I Have Been Trying to Write the whole time 
*/
function string_to_array_one(String $string)
{
	$result = [];

	$array = explode(', ', $string);

	$soft_version = array_map(function ($item) {
			if (! strstr($item, '_')) {
				return [$item];
			}
				return explode('_', $item); 
	}, $array);
	
	$softwares = array_values(array_unique(array_column($soft_version, '0')));

	foreach ($array as $key => $value) {
		
		$i = 0;

		while ($i < count($softwares)) {

			$year = ltrim(substr($value, strpos($value, '_')), '_');

			if (! strstr($value, '_') && (! in_array($value, $result)) ) {
				$result[] = $value;

			} elseif (strstr($value, '_') && strstr($value, $softwares[$i])) {

				if (! array_key_exists($softwares[$i], $result)) {
					$result[$softwares[$i]] = [];
				} elseif(! in_array($year, $result[$softwares[$i]])) {
					$result[$softwares[$i]][] = $year;						
				}

			}

			$i++;
		}

	}
		return $result;
}

                                  
                                  
// 2. Solution
function string_to_array_two(String $string)
{
	$result = [];

	$array = explode(', ', $string);

	array_walk($array, function($item, $key) use (&$result) {
		$software = substr($item, 0, strpos($item, '_'));
               $year = ltrim(substr($item, strpos($item, '_')), '_');

		if (! strpos($item, '_')) {
			$software = $item;
			$year = null;
		}

			if (! key_exists($software, $result) && $year !== null) {
				$result[$software] = [];
			} elseif ($year == null) {
				$result[] = $software;
			} else {
				$result[$software][] = $year;
			}

	});

	return $result;
}

      
      
// 3. Solution
function string_to_array_three(String $string)
{
	$array = explode(', ', $string);

	foreach ($array as $key => $value) {
		$soft_version[] = explode('_', $value); 
	}

	$result = [];

	foreach ($soft_version as $key => $value) {
			if (! array_key_exists($value[0], $result)) {

				$result[$value[0]] = [];
			
			} elseif(! in_array($value[1], $result[$value[0]])) {

				$result[$value[0]][] = $value[1];

			}

			continue;
	}

	array_map(function ($item, $key) use (&$result) {
		if (empty($item)) {
			$result[] = $key;
			unset($result[$key]);
		}
	}, $result,  array_keys($result));

	return $result;
}

      
      
// 4. Solution
function string_to_array_four(String $string)
{
	$base_array = explode(', ', $string);

	foreach ($base_array as $value) {
		if (! strpos($value, '_')) {
			$no_version[] = $value;
		  continue;
		}
		$software_list[] = substr($value, 0, strpos($value, '_'));
	}

	$software_list = array_unique($software_list);

	foreach ($base_array as $key => $base_value) {
		foreach ($software_list as $key => $software) {			

			if (strstr($base_value, $software) && strpos($base_value, '_')) {
				$year = ltrim(substr($base_value, strpos($base_value, '_')), '_');
				$result[$software][] = $year;
			}
		
		}
	}

	$result = array_merge($no_version, $result);

	array_walk($result, function($item, $key) use (&$result) {
		if (is_array($item)) {
			 $result[$key] = array_unique($item);
		}
	});

	return $result;
}