convert tab/space delimited lines into nested array

array-by-indent-2.php

<?php
/**
 * convert tab/space delimited lines into nested array
 * @link http://stackoverflow.com/q/9797261/367456
 * @author hakre <http://hakre.wordpress.com>
 */

$input = <<<STR
cat, true cat
       => domestic cat, house cat, Felis domesticus, Felis catus
           => kitty, kitty-cat, puss
           => mouser
           => alley cat
           => tom, tomcat
               => gib
           => Angora, Angora cat
           => Siamese cat, Siamese
               => blue point Siamese
       => wildcat
           => sand cat
           => European wildcat, catamountain, Felis silvestris
           => cougar, puma, catamount, mountain lion, painter, panther, Felis concolor
           => ocelot, panther cat, Felis pardalis
           => manul, Pallas's cat, Felis manul
           => lynx, catamount
               => common lynx, Lynx lynx
               => Canada lynx, Lynx canadensis
STR;

// build tree
$tree = $levels = array();
$stack[1] = &$tree;
for ($line = strtok($input, $token = "\n"); $line; $line = strtok($token)) {
    if (!preg_match('/^(?:(\s*)=> )?(.*)$/', $line, $self)) {
        continue;
    }
    array_shift($self);
    $indent = array_shift($self);
    $level = @$levels[$indent] ? : $levels[$indent] = count($levels) + 1;
    $stack[$level][] = &$self;
    $stack[$level + 1] = &$self[];
    unset($self);
}
unset($stack);

// output
tree_print($tree);
function tree_print(array $tree, $in = '') {
    echo "$in<ul>\n";
    $i = $in . '  ';
    foreach ($tree as $n)
        printf("</li>\n", printf("$i<li>$n[0]") && $n[1] && printf($i, printf("\n") & tree_print($n[1], "$i  ")));

    echo "$in</ul>\n";
}

array-by-indent-3.php

<?php
/**
 * convert tab/space delimited lines into nested array
 * @link http://stackoverflow.com/q/9797261/367456
 * @author hakre <http://hakre.wordpress.com>
 */

$input = <<<STR
cat, true cat
       => domestic cat, house cat, Felis domesticus, Felis catus
           => kitty, kitty-cat, puss
           => mouser
           => alley cat
           => tom, tomcat
               => gib
           => Angora, Angora cat
           => Siamese cat, Siamese
               => blue point Siamese
       => wildcat
           => sand cat
           => European wildcat, catamountain, Felis silvestris
           => cougar, puma, catamount, mountain lion, painter, panther, Felis concolor
           => ocelot, panther cat, Felis pardalis
           => manul, Pallas's cat, Felis manul
           => lynx, catamount
               => common lynx, Lynx lynx
               => Canada lynx, Lynx canadensis
STR;

echo_list($input);

function echo_list($string) {
    foreach ($m = array_map(function($v) use (&$l) {
        return array(@$l[$i = &$v[1]] ? : $l[$i] = count($l) + 1, $v[2]);
    }, preg_match_all('/^(?:(\s*)=> )?(.*)$/m', $string, $m, PREG_SET_ORDER) ? $m : array()) as $i => $v) {
        $pi = str_repeat("    ", $pl = @$m[$i - 1][0]); # prev
        $ni = str_repeat("    ", $nl = @$m[$i + 1][0]); # next
        (($v[0] - $pl) > 0) && printf("$pi<ul>\n");     # is child of prev
        echo '  ' . str_repeat("    ", $v[0] - 1), "<li>$v[1]"; # output self
        if (!$close = (($nl - $v[0]) * -1)) echo "</li>\n"; # has sibling
        else if ($close < 0) echo "\n";                     # has children
        else for (printf("</li>\n$ni" . str_repeat("    ", $close - 1) . "</ul>\n"); --$close;) # is last child
                echo $ni, $nn = str_repeat("    ", $close - 1), "  </li>\n",
                     $ni, $nn, "</ul>\n";
    }
}

array-by-indent.php

<?php
/**
 * convert tab/space delimited lines into nested array
 * @link http://stackoverflow.com/q/9797261/367456
 * @author hakre <http://hakre.wordpress.com>
 */

$input = <<<STR
cat, true cat
       => domestic cat, house cat, Felis domesticus, Felis catus
           => kitty, kitty-cat, puss
           => mouser
           => alley cat
           => tom, tomcat
               => gib
           => Angora, Angora cat
           => Siamese cat, Siamese
               => blue point Siamese
       => wildcat
           => sand cat
           => European wildcat, catamountain, Felis silvestris
           => cougar, puma, catamount, mountain lion, painter, panther, Felis concolor
           => ocelot, panther cat, Felis pardalis
           => manul, Pallas's cat, Felis manul
           => lynx, catamount
               => common lynx, Lynx lynx
               => Canada lynx, Lynx canadensis
STR;

/**
 * Levels for indent strings
 */
class Levels
{
    private $levels = array();

    public function __invoke($str)
    {
        $number = strlen($str);

        $key = array_search($number, $this->levels, true);
        if ($key !== false) {
            return $key;
        }

        $key = count($this->levels);
        if ($key && $number < $this->levels[$key - 1]) {
            throw new InvalidArgumentException(sprintf(
                'The number given %d is not a level yet but below the range of levels which ends at %d.',
                $number, $this->levels[$key - 1]
            ));
        }

        $this->levels[$key] = $number;
        return $key;
    }
}

/**
 * preg match as array
 *
 * @param $string
 * @param string $pattern pcre regular expression pattern.
 * @return array
 */
$matches = function($string, $pattern)
{
    return preg_match_all($pattern, $string, $matches, PREG_SET_ORDER)
        ? $matches : array();
};

$map = function(Levels $levels)
{
    return function (array $match) use ($levels)
    {
        list(, $indent, $name) = $match;
        $level = $levels($indent);
        return array($level, $name);
    };
};
$map = $map(new Levels());

$tree = array();
$stack = function(array &$tree)
{
    $stack[] = &$tree;
    return function($level, $element) use (&$stack)
    {
        $self = array($element, array());
        $stack[$level][] = &$self;
        $stack[$level + 1] = &$self[1];
    };
};
$push = $stack($tree);

foreach ($matches($input, '/^(?:(\s*)=> )?(.*)$/m') as $match) {
    list($level, $element) = $map($match);
    $push($level, $element);
}

class TreeIterator extends ArrayIterator implements RecursiveIterator
{
    private $current;

    public function __construct($node)
    {
        parent::__construct($node);
    }

    public function current()
    {
        $this->current = parent::current();
        return $this->current[0];
    }

    public function hasChildren()
    {
        return !empty($this->current[1]);
    }

    public function getChildren()
    {
        return new self($this->current[1]);
    }
}

$treeIterator = new RecursiveTreeIterator(
    new TreeIterator($tree));

foreach ($treeIterator as $val) echo $val, "\n";

exemplary tree

array (
  0 => 
  array (
    0 => 'cat, true cat',
    1 => 
    array (
      0 => 
      array (
        0 => 'domestic cat, house cat, Felis domesticus, Felis catus',
        1 => 
        array (
          0 => 
          array (
            0 => 'kitty, kitty-cat, puss',
            1 => NULL,
          ),
          1 => 
          array (
            0 => 'mouser',
            1 => NULL,
          ),
          2 => 
          array (
            0 => 'alley cat',
            1 => NULL,
          ),
          3 => 
          array (
            0 => 'tom, tomcat',
            1 => 
            array (
              0 => 
              array (
                0 => 'gib',
                1 => NULL,
              ),
            ),
          ),
          4 => 
          array (
            0 => 'Angora, Angora cat',
            1 => NULL,
          ),
          5 => 
          array (
            0 => 'Siamese cat, Siamese',
            1 => 
            array (
              0 => 
              array (
                0 => 'blue point Siamese',
                1 => NULL,
              ),
            ),
          ),
        ),
      ),
      1 => 
      array (
        0 => 'wildcat',
        1 => 
        array (
          0 => 
          array (
            0 => 'sand cat',
            1 => NULL,
          ),
          1 => 
          array (
            0 => 'European wildcat, catamountain, Felis silvestris',
            1 => NULL,
          ),
          2 => 
          array (
            0 => 'cougar, puma, catamount, mountain lion, painter, panther, Felis concolor',
            1 => NULL,
          ),
          3 => 
          array (
            0 => 'ocelot, panther cat, Felis pardalis',
            1 => NULL,
          ),
          4 => 
          array (
            0 => 'manul, Pallas\'s cat, Felis manul',
            1 => NULL,
          ),
          5 => 
          array (
            0 => 'lynx, catamount',
            1 => 
            array (
              0 => 
              array (
                0 => 'common lynx, Lynx lynx',
                1 => NULL,
              ),
              1 => 
              array (
                0 => 'Canada lynx, Lynx canadensis',
                1 => NULL,
              ),
            ),
          ),
        ),
      ),
    ),
  ),
)