KNN_3NN

<?php

// Simulated ratings for books from input_database sample
 // array (ratings:(0-->5), 'Name of book")
$input_data = array(                     // 2D array[indexes]
    array(0, 'Van Helsing'),      //  [0]
    array(3, 'Dracula'),           // [1]
    array(2, 'The Pearl'),        //  [2]
    array(4, 'Pocahontas'),      //   [3]
    array(0, 'How to be good'),   //  [4]
    array(4, 'I know how to love'),  // [5]
    array(2, 'How to be millionaire'),  // [6]
    array(5, 'Eat, pray and love'),   // [7]
    array(4, 'How to follow God'),   // [8]
        array(5, 'Intro to Philosophy'), // [9]
        array(2, 'Intro Algorithms'),   // [10]
        array(2, 'How to happy'),      // [11]
        array(4, 'How to have sex'),   // [12]
        array(0, 'Quantum Mechanics'),  //[13]
        array(3, 'Purpose Driven live') // [14]
);


// Calculat the distances or differences of points
$distance_matrix = $input_data;

//array_walk — Apply a user function to every member of an array
array_walk($distance_matrix, 'Euclid_Distance', $input_data);


// Specify the data point index, it would compute the #3NN automatically
$neighbors = KNN($distance_matrix, 13);
echo assoc_book_name($input_data, $neighbors); // red


// This is necessary for calculating the distance between ratings values
function Euclid_Distance(&$sourceCoords, $sourceKey, $input_data)
{
    $distance_matrix = array();
    list ($Xi, $Yi) = $sourceCoords;

    foreach ($input_data as $destinationKey => $destinationCoords)
        {
        // Same point, ignore
        if ($sourceKey == $destinationKey)
                {
            continue;
        }
        list ($X_2, $Y_2) = $destinationCoords;
        //$distance_matrix[$destinationKey] = abs(pow($x1 - $x2, 2) + pow($y1 - $y2, 2));
                $distance_matrix[$destinationKey] = sqrt(pow($Xi - $X_2, 2) + pow($Yi - $Y_2, 2));
    }
    asort($distance_matrix);
    $sourceCoords = $distance_matrix;
}

// Returns n-nearest neighbors

function KNN($distance_matrix, $N)
{                                             // 3NN, K = 3
    return array_slice($distance_matrix[$N], 0, 3, true);
}

/*
  Gets result label from associated input_data
 */
function assoc_book_name($input_data, $neighbors)
{
  $results = array();
  $neighbors = array_keys($neighbors);

  foreach ($neighbors as $neighbor)
   {                                 // 2 (xi, yi) before, look at 1 data point
        $results[] = $input_data[$neighbor][1];
   }

    $val = array_count_values($results);
    $val = array_flip($val);
    ksort($val);
    return array_pop($val);
}