303 lines
11 KiB
PHP
303 lines
11 KiB
PHP
<?php
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require_once("JsonStorageBox.php");
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if (!function_exists('stats_standard_deviation')) {
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/**
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* This user-land implementation follows the implementation quite strictly;
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* it does not attempt to improve the code or algorithm in any way. It will
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* raise a warning if you have fewer than 2 values in your array, just like
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* the extension does (although as an E_USER_WARNING, not E_WARNING).
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*
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* @param array $a
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* @param bool $sample [optional] Defaults to false
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* @return float|bool The standard deviation or false on error.
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*/
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function stats_standard_deviation(array $a, $sample = false) {
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$n = count($a);
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if ($n === 0) {
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trigger_error("The array has zero elements", E_USER_WARNING);
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return false;
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}
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if ($sample && $n === 1) {
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trigger_error("The array has only 1 element", E_USER_WARNING);
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return false;
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}
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$mean = array_sum($a) / $n;
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$carry = 0.0;
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foreach ($a as $val) {
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$d = ((double) $val) - $mean;
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$carry += $d * $d;
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};
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if ($sample) {
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--$n;
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}
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return sqrt($carry / $n);
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}
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}
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/**
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* A serialisable BK-Tree Implementation.
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* Ref: https://nullwords.wordpress.com/2013/03/13/the-bk-tree-a-data-structure-for-spell-checking/
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*/
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class BkTree
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{
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private $box = null;
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private $nodes = [];
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// private $touched_ids = [];
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private $cost_insert = 1;
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private $cost_delete = 1;
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private $cost_replace = 1;
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public function __construct($filename) {
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$this->box = new JsonStorageBox($filename);
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}
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/**
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* A utility function for calculating edit distance.
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* Warning: Do not use this internally! It is *slow*. It's much faster to do this directly. This exists only for external use.
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* @param string $a The first string.
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* @param string $b The second string to compare against.
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* @return int The computed edit distance.
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*/
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public function edit_distance(string $a, string $b) : int {
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return levenshtein($a, $b, $this->cost_insert, $this->cost_replace, $this->cost_delete);
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}
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private function get_node_count() : int {
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if(!$this->box->has("node_count"))
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$this->set_node_count(0);
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return $this->box->get("node_count");
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}
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private function set_node_count(int $value) {
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$this->box->set("node_count", $value);
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}
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private function increment_node_count() {
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$this->box->set("node_count", $this->box->get("node_count") + 1);
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}
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/**
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* Adds a string to the tree.
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* @param string $string The string to add.
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* @return int The depth at which the new node was added.
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*/
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public function add(string $string) : int {
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// FUTURE: When we support deletes, we'll need to ensure that the root node is handled correctly
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if(!$this->box->has("node|0")) {
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$new = new stdClass();
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$new->value = $string;
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$new->children = new stdClass(); // [ "id" => int, "distance" => int ]
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$this->box->set("node|0", $new);
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$this->touched_ids[] = 0;
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$this->increment_node_count();
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return 0;
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}
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// if($string == "bunny") echo("\nStart $string\n");
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$next_node = $this->box->get("node|0"); // Grab the root to start with
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$next_node_id = 0;
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$depth = 0; $visted = 0;
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while(true) {
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$visted++;
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$distance = levenshtein($string, $next_node->value, $this->cost_insert, $this->cost_replace, $this->cost_delete);
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// if($string == "bunny") echo("$visted: Visiting $next_node->value, distance $distance (child distances ".implode(", ", array_map(function($el) { return $el->distance; }, $next_node->children)).")\n");
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if(isset($next_node->children->$distance)) {
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$child_id = $next_node->children->$distance;
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$next_node = $this->box->get("node|$child_id");
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$next_node_id = $child_id;
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// if($string == "cake") echo("Identical distance as {$next_node["value"]}, restarting loop\n");
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$depth++;
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continue; // Continue on the outer while loop
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}
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// if($string == "bunny") echo("Inserting on $next_node->value\n");
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// If we got here, then no existing children have the same edit distance
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// Note that here we don't push to avoid the overhead from either array_push() (considerable) or count() (also considerable).
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// Create the new child node
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$new_id = $this->get_node_count();
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$this->box->set("node|$new_id", (object) [
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"value" => $string,
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"children" => new stdClass()
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]);
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// Create the edge that points from the existing node to the new node
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$next_node->children->$distance = $new_id;
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$this->box->set("node|$next_node_id", $next_node);
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$this->increment_node_count();
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break;
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}
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return $depth;
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}
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/**
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* Removes a string from the tree.
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* @param string $string The string to remove.
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* @return bool Whether the removal was successful.
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*/
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public function remove(string $string) : bool {
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throw new Error("Error: Not implemented");
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// TODO: Remove a node from the tree.
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// 1. Delete the connection from parent -> target
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// 2. Iterate over the target's children (if any) and re-hang them from the parent
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// NOTE: We need to be careful that the characteristics of the tree are preserved. We should test this by tracing a node's location in the tree and purposefully removing nodes in the chain and see if the results returned as still the same
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}
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/**
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* Convenience function that returns just the first result when looking up a string.
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* @param string $string The string to lookup
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* @param integer $distance The maximum edit distance to search.
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* @return string|null The first matching string, or null if no results were found.
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*/
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public function lookup_one(string $string, int $distance = 1) {
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$result = $this->lookup($string, $distance, 1);
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if(empty($result)) return null;
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return $result[0];
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// foreach($this->lookup($string, $distance) as $item)
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// return $item;
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}
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/**
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* Generator that walks the BK-Tree and iteratively yields results.
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* TODO: Refactor this to use an array, since generators are ~
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* @param string $string The search string.
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* @param integer $max_distance The maximum edit distance to search.
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* @param integer $count The number of results to return. 0 = All results found. Note that results will be in a random order.
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* @return Generator<string> Iteratively yielded similar resultant strings from the BK-Tree.
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*/
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public function lookup(string $string, int $max_distance = 1, int $count = 0) {
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if($this->get_node_count() == 0) return null;
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$result = []; $result_count = 0;
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$stack = [ $this->box->get("node|0") ];
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$stack_top = 0;
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// https://softwareengineering.stackexchange.com/a/226162/58491
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while($stack_top >= 0) {
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// Take the topmost node off the stack
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$node_current = $stack[$stack_top];
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unset($stack[$stack_top]);
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$stack_top--;
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$distance = levenshtein($string, $node_current->value, $this->cost_insert, $this->cost_replace, $this->cost_delete);
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/*
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echo("[lookup] Visiting $node_current->value (distance $distance, child distances ".implode(", ", array_map(function($el) { return $el->distance; }, $node_current->children)).")\n");
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if(in_array($node_current->value, ["worlds", "domicil", "mealiest", "stopgaps", "pibroch", "upwardly", "nontruth", "vizoring"])) {
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echo("[lookup] Children: ".implode(", ", array_map(function($el) {
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return "$el->distance: ".$this->box->get("node|$el->id")->value;
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}, $node_current->children))."\n");
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}
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if($node_current->value == "bunny") exit();
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*/
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// If the edit distance from the target string to this node is within the tolerance, yield it
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if($distance <= $max_distance) {
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// readline("press any key to continue");
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$result[] = $node_current->value;
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if($count != 0 && $result_count >= $count) break;
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// yield $node_current["value"];
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}
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// Adding the key here speeds it up, apparently
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// Ref: https://phpbench.com/
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for($child_distance = $distance - $max_distance; $child_distance <= $distance + $max_distance; $child_distance++) {
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if(!isset($node_current->children->$child_distance))
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continue;
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// echo("[lookup] Recursing on child ".$this->box->get("node|$child->id")->value." (distance $child->distance)\n");
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// Push the node onto the stack
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// Note that it doesn't actually matter that the stack isn't an accurate representation of ancestor nodes at any given time here. The stack is really a hybrid between a stack and a queue, having features of both.
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$stack_top++;
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$stack[$stack_top] = $this->box->get("node|{$node_current->children->$child_distance}");
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}
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}
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return $result;
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}
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/**
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* Calculate statistics about the BK-Tree.
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* Useful for analysing a tree's structure.
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* If the tree isn't balanced, you may need to insert items in a different order.
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* @return array An array of statistics about this BK-Tree.
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*/
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public function stats() {
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$result = [
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"depth_max" => 0,
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"depth_min_leaf" => INF,
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"depth_average" => 0,
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"depth_average_noleaf" => 0,
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"depth_standard_deviation" => [],
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"child_count_average" => 0,
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"child_count_max" => 0,
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"nodes" => $this->get_node_count(),
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"leaves" => 0,
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"non_leaves" => 0
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];
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$start_time = microtime(true);
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$stack = [ [ "node" => $this->box->get("node|0"), "depth" => 0 ] ];
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// https://softwareengineering.stackexchange.com/a/226162/58491
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while(!empty($stack)) {
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// Take the top-most node off the stack
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$current = array_pop($stack);
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// echo("Visiting "); var_dump($current);
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// Operate on the node
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$result["depth_standard_deviation"][] = $current["depth"];
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$result["depth_average"] += $current["depth"];
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if($current["depth"] > $result["depth_max"])
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$result["depth_max"] = $current["depth"];
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if(empty($current["node"]->children) && $current["depth"] < $result["depth_min_leaf"])
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$result["depth_min_leaf"] = $current["depth"];
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$child_count = count((array)($current["node"]->children));
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$result["child_count_average"] += $child_count;
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if($child_count > $result["child_count_max"])
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$result["child_count_max"] = $child_count;
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if($child_count > 0) {
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$result["depth_average_noleaf"] += $current["depth"];
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$result["non_leaves"]++;
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}
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else
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$result["leaves"]++;
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// Iterate over the child nodes
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foreach($current["node"]->children as $child_distance => $child_id) {
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$stack[] = [
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"node" => $this->box->get("node|$child_id"),
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"depth" => $current["depth"] + 1
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];
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}
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}
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$result["depth_average"] /= $result["nodes"];
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$result["depth_average_noleaf"] /= $result["non_leaves"];
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$result["child_count_average"] /= $result["nodes"];
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$result["depth_standard_deviation"] = stats_standard_deviation($result["depth_standard_deviation"]);
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$result["time_taken"] = microtime(true) - $start_time;
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return $result;
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}
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/**
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* Saves changes to the tree back to disk.
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* @return void
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*/
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public function close() {
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$this->box->close();
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}
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}
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