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Starbeamrainbowlabs
be8595bc44
There's also a bug in the deletion logic in that if the root node is deleted (if it doesn't crash first), then it's all over and it's broken.
384 lines
13 KiB
PHP
384 lines
13 KiB
PHP
<?php
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register_module([
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"name" => "Did you mean? support",
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"version" => "0.1",
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"author" => "Starbeamrainbowlabs",
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"description" => "Ever searched for something but couldn't find it because you couldn't spell it correctly? This module is for you! It adds spelling correction for search queries based on the words in the inverted search index.",
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"id" => "lib-storage-box",
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"depends" => [ "lib-search-engine" ],
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"code" => function() {
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}
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]);
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/**
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* Calculates the standard deviation of an array of numbers.
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* @source https://stackoverflow.com/a/57694168/1460422
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* @param array $array The array of numbers to calculate the standard deviation of.
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* @return float The standard deviation of the numbers in the given array.
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*/
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function standard_deviation(array $array): float {
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$size = count($array);
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$mean = array_sum($array) / $size;
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$squares = array_map(function ($x) use ($mean) {
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return pow($x - $mean, 2);
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}, $array);
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return sqrt(array_sum($squares) / ($size - 1));
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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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private $box = null;
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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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* @param int $starting_node_id The id fo node to start insertion from. Defaults to 0 - for internal use only.
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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 $starting_node_id = 0) : int {
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if(!$this->box->has("node|0")) {
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// If the root node of the tree doesn't exist, create it
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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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$this->increment_node_count();
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return 0;
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}
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if(!$this->box->has("node|$starting_node_id"))
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throw new Exception("Error: Failed to find node with id $starting_node_id to begin insertion");
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// if($string == "bunny") echo("\nStart $string\n");
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$next_node = $this->box->get("node|$starting_node_id"); // Grab the root to start with
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$next_node_id = $starting_node_id;
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$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, $this->cost_delete);
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if(isset($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 = $child_id;
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$depth++;
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continue; // Continue on the outer while loop
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}
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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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* BUG: If this deletes the root node, then it's all over and it will crash
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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 $string) : bool {
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$stack = [ [ "node" => $this->box->get("node|0"), "id" => 0 ] ];
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$node_target = $stack[0]["node"];
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$node_target_id = 0;
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while($node_target->value !== $string) {
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$distance = levenshtein($string, $node_target->value, $this->cost_insert, $this->cost_replace, $this->cost_delete);
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// Failed to recurse to find the node with the value in question
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if(!isset($node_target->children->$distance))
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return false;
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$node_target_id = $node_target->children->$distance;
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$node_target = $this->box->get("node|$node_target_id");
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$stack[] = [ "node" => $node_target, "id" => $node_target_id ];
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}
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// The last item but 1 on the stack is the parent node
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$parent = $stack[count($stack) - 2];
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// 1. Delete the connection from parent -> target
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foreach($parent["node"]->children as $distance => $id) {
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if($id == $node_target_id) {
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unset($parent["node"]->children->$distance);
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break;
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}
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}
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// Save the parent node's back to disk
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// Note that we do this *before* sorting out the orphans, since it's possible that $this->add() will modify it further
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$this->box->set("node|{$parent["id"]}", $parent["node"]);
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// 2. Iterate over the target's children (if any) and re-hang them from the parent
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// Hang the now orphaned children and all their decendants from the parent
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foreach($node_target->children as $distance => $id) {
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$orphan = $this->box->get("node|$id");
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$substack = [ [ "node" => $orphan, "id" => $id ] ]; $substack_top = 0;
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while($substack_top >= 0) {
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$next = $substack[$substack_top];
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unset($substack[$substack_top]);
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$substack_top--;
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$this->box->delete("node|{$next["id"]}"); // Delete the orphan node
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$this->add($next["node"]->value, $parent["id"]); // Re-hang it from the parent
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foreach($next["node"]->children as $distance => $sub_id) {
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$substack[++$substack_top] = [
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"node" => $this->box->get("node|$sub_id"),
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"id" => $sub_id
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];
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}
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}
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}
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// Delete the target node
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$this->box->delete("node|$node_target_id");
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return true;
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}
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public function trace(string $string) {
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$stack = [
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(object) [ "node" => $this->box->get("node|0"), "id" => 0 ]
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];
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$node_target = $stack[0]->node;
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while($node_target->value !== $string) {
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$distance = levenshtein($string, $node_target->value, $this->cost_insert, $this->cost_replace, $this->cost_delete);
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// var_dump($node_target);
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// Failed to recurse to find the node with the value in question
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if(!isset($node_target->children->$distance))
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return null;
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$node_target_id = $node_target->children->$distance;
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$node_target = $this->box->get("node|$node_target_id");
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$stack[] = (object) [ "node" => $node_target, "id" => $node_target_id ];
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}
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return $stack;
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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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}
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/**
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* Generator that walks the BK-Tree and iteratively yields results.
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* Note that the returned array is *not* sorted.
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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 array<string> 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, $this->cost_delete);
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// If the edit distance from the target string to this node is within the tolerance, store it
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if($distance <= $max_distance) {
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$result[] = $node_current->value;
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$result_count++;
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if($count != 0 && $result_count >= $count) break;
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}
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for($child_distance = $distance - $max_distance; $child_distance <= $distance + $max_distance; $child_distance++) {
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if(!isset($node_current->children->$child_distance))
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continue;
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$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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// 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"] = standard_deviation($result["depth_standard_deviation"]);
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$result["time_taken"] = microtime(true) - $start_time;
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return $result;
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}
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/**
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* Iteratively walks the BkTree.
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* Warning: This is *slow*
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* @return Generator<stdClass> A generator that iteratively walks the tree and yields every item therein that's connected to the root node.
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*/
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public function walk() {
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$stack = [ (object)[
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"id" => 0,
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"node" => $this->box->get("node|0"),
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"parent_id" => -1,
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"parent" => null,
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"depth" => 0
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] ];
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$stack_top = 0;
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// https://softwareengineering.stackexchange.com/a/226162/58491
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while(!empty($stack)) {
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// Take the topmost node off the stack
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$current = $stack[$stack_top];
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unset($stack[$stack_top]);
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$stack_top--;
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// echo("Visiting "); var_dump($current);
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yield $current;
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// Iterate over the child nodes
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foreach($current->node->children as $child_distance => $child_id) {
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$stack_top++;
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$stack[$stack_top] = (object) [
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"id" => $child_id,
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"node" => $this->box->get("node|{$current->node->children->$child_distance}"),
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"parent_id" => $current->id,
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"parent" => $current->node,
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"depth" => $current->depth + 1
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];
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}
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}
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}
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/**
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* Saves changes to the tree back to disk.
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* @return void
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*/
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public function close() {
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$this->box->close();
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}
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}
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?>
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