Recursive

function countdown(i) {
    console.log(i)  if (i <= 1) {  // base case
        return;
    } else {     // recursive case
        countdown(i - 1);
    }
}

countdown(5);    // This is the initial call to the function.

 {"countries":[
    {
        "name":"USA",

        "grandfathers":[
            {
                "gFName":"Steve",
                "grandfathersKid":[
                    {
                        "gFKName": "Linda",
                        "kid": [{
                            "name": "Steve JR", 
                            "friends": [{
                                "name": "Kriss|John|Martin|Steven"
                            }]
                        }
                        ]
                    }

                ]
            }
        ]
    }
]}

<?php
function factorial ($number, $factorial = 1) {
    if ($number < 0) {
        throw new InvalidArgumentException('Number cannot be less than zero (0)');
    }
    if ($number == 0) {
        return $factorial;
    }
    else {
        return factorial($number - 1, $factorial * $number);
    }
}

$stmnt = $pdo->prepare("
    SELECT dog_id, dog_name, dog_sex, mother_id, father_id
    FROM tbl_dogs
    WHERE dog_id = ?
");

fetchDogRecursive($yourDogId);

function fetchDogRecursive($dogId)
{
    $stmnt->execute(array($dogId));

    $dogData = $stmnt->fetchAll(PDO::FETCH_ASSOC)[0];

    $dog = array(
        'id' => $dogData['dog_id'],
        'name' => $dogData['dog_name'],
        'mother' => null,
        'father' => null
    );

    if($dogData['mother_id'] !== null) {
        $dog['mother'] = fetchDogRecursive($dogData['mother_id']);
    }

    if($dogData['father_id'] !== null) {
        $dog['father'] = fetchDogRecursive($dogData['father_id']);
    }

    return $dog;
}

function recursive($array, $level = 0)
{
    foreach($array as $key => $value)
	{
        
		if (!is_array($value) && $key == "tag") { echo str_repeat(" ", $level), "[".$value."]", ''; }
		
		//If $value is an array.
        if(is_array($value))
		{
			//We need to loop through it.
            recursive($value, $level + 1);
        } 
		else
		{
            //It is not an array, so print it out.			
			if ($key == "tag") { echo "[/".$value."]", '<br>'; }
						
        }
    }
}

$tree_2 = recursive($tree_1);

echo $tree_2;

<?php

function factorial( $n ) {

  // Base case
  if ( $n == 0 ) {
    echo "Base case: $n = 0. Returning 1...<br>";
    return 1;
  }

  // Recursion
  echo "$n = $n: Computing $n * factorial( " . ($n-1) . " )...<br>";
  $result = ( $n * factorial( $n-1 ) );
  echo "Result of $n * factorial( " . ($n-1) . " ) = $result. Returning $result...<br>";
  return $result;
}

echo "The factorial of 5 is: " . factorial( 5 );

?>

define("MAX_GEN",5);

function detail($number) {
    $d = mysql_query("select * from table where number = '$number'");
    if(mysql_num_rows($d) == 0) {
        $p[name] = "N/A";
        $p[number] = "N/A";
        $p[m_number] = "N/A";
        $p[f_number] = "N/A";
    }
    else $p = mysql_fetch_assoc($d);
    return $p;
}

function gen($number, $generation = 0, $out) {

    if ($generation >= MAX_GEN) {
        return false;
    }

    $record = detail($number);

    if ($generation == 0) $out[0][] = $record; // first man

    $generation++; // next generation

    if (!$out[$generation] && ($generation != MAX_GEN)) $out[$generation] = array();

    $x_mother = gen($record[m_number], $generation ); // continue with mother
    $x_father = gen($record[f_number], $generation ); // continue with father

    if ($out[$generation]) {
        $out[$generation][] = $x_mother;
        $out[$generation][] = $x_father;
    }
    return $out;
}

<?php
    $dates = array
    (
        '0' => "2013-02-18 05:14:54",
        '1' => "2013-02-12 01:44:03",
        '2' => "2013-02-05 16:25:07",
        '3' => "2013-01-29 02:00:15",
        '4' => "2013-01-27 18:33:45"
    );

    function closest($dates, $findate)
    {
        $newDates = array();

        foreach($dates as $date)
        {
            $newDates[] = strtotime($date);
        }

        echo "<pre>";
        print_r($newDates);
        echo "</pre>";

        sort($newDates);
        foreach ($newDates as $a)
        {
            if ($a >= strtotime($findate))
                return $a;
        }
        return end($newDates);
    }

    $values = closest($dates, date('2013-02-04 14:11:16'));
    echo date('Y-m-d h:i:s', $values);
?>

$arr = [300, 600, 900, 1200];
$number = 920;
$deltas = array_reduce(
    $arr, 
    function($t, $v) use ($number) { 
        $t[$v] = abs($v - $number); 
        return $t; 
    },
    []
);
asort($deltas);
echo array_keys($deltas)[0];