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mahdi
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<h1 class="post-title"><p>Autocomplete using Tries</p>
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</h1>
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<span>Jul 24, 2015</span>
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• <span>Reading time: 8 minutes</span>
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<article class="post-content">
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<p>In this article, I’m going over creating an autocompletion/prediction system using a data-structure called Trie, it’s fast and easy to customize.</p>
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<h1 id="trie">Trie</h1>
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<p><a href="https://en.wikipedia.org/wiki/Trie">Trie</a> is a simple data-structure most commonly used as a dictionary, it looks like so:</p>
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<p><img src="/img/trie.jpg" alt="Trie" /></p>
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<p>As you see, it’s just a <em>tree</em>, a set of nodes connected to other [child] nodes, but the nodes have a special relationship:</p>
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<p>Each child node extends it’s parent with one extra character.</p>
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<figure class="highlight"><pre><code class="language-javascript" data-lang="javascript"><span class="c1">// Something like this</span>
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<span class="nx">child</span><span class="p">.</span><span class="nx">value</span> <span class="o">=</span> <span class="nx">parent</span><span class="p">.</span><span class="nx">value</span> <span class="o">+</span> <span class="dl">'</span><span class="s1">c</span><span class="dl">'</span><span class="p">;</span></code></pre></figure>
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<p>It’s pretty easy to traverse this tree and predict the next possible words.</p>
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<h2 id="implementation">Implementation</h2>
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<p>We’re going to use ES6 classes to create our <code class="language-plaintext highlighter-rouge">Trie</code> and <code class="language-plaintext highlighter-rouge">Node</code> classes.</p>
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<p>Let’s start with our simple Node class:</p>
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<figure class="highlight"><pre><code class="language-javascript" data-lang="javascript"><span class="kd">class</span> <span class="nx">Node</span> <span class="p">{</span>
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<span class="kd">constructor</span><span class="p">(</span><span class="nx">value</span> <span class="o">=</span> <span class="dl">''</span><span class="p">)</span> <span class="p">{</span>
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<span class="k">this</span><span class="p">.</span><span class="nx">value</span> <span class="o">=</span> <span class="nx">value</span><span class="p">;</span>
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<span class="k">this</span><span class="p">.</span><span class="nx">children</span> <span class="o">=</span> <span class="p">[];</span>
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<span class="p">}</span>
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<span class="p">}</span></code></pre></figure>
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<p>Unlike <a href="https://en.wikipedia.org/wiki/Binary_tree">binary trees</a> where each node has a left and right child, Trie nodes don’t necessarily have a limit on how many children they can have.</p>
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<p>Trie class:</p>
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<figure class="highlight"><pre><code class="language-javascript" data-lang="javascript"><span class="kd">class</span> <span class="nx">Trie</span> <span class="p">{</span>
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<span class="kd">constructor</span><span class="p">()</span> <span class="p">{</span>
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<span class="k">this</span><span class="p">.</span><span class="nx">root</span> <span class="o">=</span> <span class="k">new</span> <span class="nx">Node</span><span class="p">();</span>
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<span class="p">}</span>
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<span class="nx">add</span><span class="p">(</span><span class="nx">value</span><span class="p">,</span> <span class="nx">parent</span> <span class="o">=</span> <span class="k">this</span><span class="p">.</span><span class="nx">root</span><span class="p">)</span> <span class="p">{</span>
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<span class="k">for</span> <span class="p">(</span><span class="kd">let</span> <span class="nx">i</span> <span class="o">=</span> <span class="mi">0</span><span class="p">,</span> <span class="nx">len</span> <span class="o">=</span> <span class="nx">value</span><span class="p">.</span><span class="nx">length</span><span class="p">;</span> <span class="nx">i</span> <span class="o"><</span> <span class="nx">len</span><span class="p">;</span> <span class="nx">i</span><span class="o">++</span><span class="p">)</span> <span class="p">{</span>
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<span class="kd">let</span> <span class="nx">node</span> <span class="o">=</span> <span class="nx">parent</span><span class="p">.</span><span class="nx">children</span><span class="p">.</span><span class="nx">find</span><span class="p">(</span><span class="nx">child</span> <span class="o">=></span> <span class="nx">child</span><span class="p">.</span><span class="nx">value</span><span class="p">[</span><span class="nx">i</span><span class="p">]</span> <span class="o">===</span> <span class="nx">value</span><span class="p">[</span><span class="nx">i</span><span class="p">]);</span>
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<span class="k">if</span> <span class="p">(</span><span class="o">!</span><span class="nx">node</span><span class="p">)</span> <span class="p">{</span>
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<span class="nx">node</span> <span class="o">=</span> <span class="k">new</span> <span class="nx">Node</span><span class="p">(</span><span class="nx">value</span><span class="p">.</span><span class="nx">slice</span><span class="p">(</span><span class="mi">0</span><span class="p">,</span> <span class="nx">i</span> <span class="o">+</span> <span class="mi">1</span><span class="p">));</span>
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<span class="nx">parent</span><span class="p">.</span><span class="nx">children</span><span class="p">.</span><span class="nx">push</span><span class="p">(</span><span class="nx">node</span><span class="p">);</span>
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<span class="p">}</span>
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<span class="nx">parent</span> <span class="o">=</span> <span class="nx">node</span><span class="p">;</span>
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<span class="p">}</span>
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<span class="k">return</span> <span class="nx">parent</span><span class="p">;</span>
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<span class="p">}</span>
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<span class="nx">find</span><span class="p">(</span><span class="nx">value</span><span class="p">,</span> <span class="nx">parent</span> <span class="o">=</span> <span class="k">this</span><span class="p">.</span><span class="nx">root</span><span class="p">)</span> <span class="p">{</span>
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<span class="k">for</span> <span class="p">(</span><span class="kd">let</span> <span class="nx">i</span> <span class="o">=</span> <span class="mi">0</span><span class="p">,</span> <span class="nx">len</span> <span class="o">=</span> <span class="nx">value</span><span class="p">.</span><span class="nx">length</span><span class="p">;</span> <span class="nx">i</span> <span class="o"><</span> <span class="nx">len</span><span class="p">;</span> <span class="nx">i</span><span class="o">++</span><span class="p">)</span> <span class="p">{</span>
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<span class="nx">parent</span> <span class="o">=</span> <span class="nx">parent</span><span class="p">.</span><span class="nx">children</span><span class="p">.</span><span class="nx">find</span><span class="p">(</span><span class="nx">child</span> <span class="o">=></span> <span class="nx">child</span><span class="p">.</span><span class="nx">value</span><span class="p">[</span><span class="nx">i</span><span class="p">]</span> <span class="o">===</span> <span class="nx">value</span><span class="p">[</span><span class="nx">i</span><span class="p">]);</span>
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<span class="k">if</span> <span class="p">(</span><span class="o">!</span><span class="nx">parent</span><span class="p">)</span> <span class="k">return</span> <span class="kc">null</span><span class="p">;</span>
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<span class="p">}</span>
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<span class="k">return</span> <span class="nx">parent</span><span class="p">;</span>
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<span class="p">}</span>
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<span class="p">}</span></code></pre></figure>
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<p>Every Trie must have a root node with empty value, that’s how our single-character nodes follow the rule of Tries.</p>
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<p>Ok, our first method, <code class="language-plaintext highlighter-rouge">add</code> handles adding a value to the trie, creating necessary parent nodes for our value.
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At each iteration, we compare the <code class="language-plaintext highlighter-rouge">i</code>th character of our value, with <code class="language-plaintext highlighter-rouge">i</code>th character of current node’s children’s value,
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if we find one, we continue to search the next branch, else, we create a node with <code class="language-plaintext highlighter-rouge">value.slice(0, i + 1)</code> and move onto the created node.</p>
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<p>It might be a little hard to grasp at first, so I created a visualization of this method to help you understand it easier, take a look:
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<a href="https://mdibaiee.github.io/autocomplete-trie/demo/add.html">Trie Visualization</a></p>
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<p>Then we have our find method, which searches for the given value in the trie. The algorithm for searching is the same, comparing by index and moving to the next branch.</p>
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<h1 id="example">Example</h1>
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<p>That’s it for our simple Trie class, now let’s create an actual input with autocomplete functionality using our Trie.</p>
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<figure class="highlight"><pre><code class="language-html" data-lang="html"><span class="nt"><input></span>
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<span class="nt"><div</span> <span class="na">class=</span><span class="s">'results'</span><span class="nt">></span>
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<span class="nt"></div></span></code></pre></figure>
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<p>I put some random names and stuff into three categories, results: <a href="https://mdibaiee.github.io/autocomplete-trie/demo/data.json">data.json</a></p>
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<p>Now we have to create a Trie of our data:</p>
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<figure class="highlight"><pre><code class="language-javascript" data-lang="javascript"><span class="kd">const</span> <span class="nx">trie</span> <span class="o">=</span> <span class="k">new</span> <span class="nx">Trie</span><span class="p">();</span>
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<span class="kd">let</span> <span class="nx">data</span> <span class="o">=</span> <span class="p">{...};</span> <span class="c1">// read from data.json</span>
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<span class="k">for</span> <span class="p">(</span><span class="kd">let</span> <span class="nx">category</span> <span class="k">in</span> <span class="nx">data</span><span class="p">)</span> <span class="p">{</span>
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<span class="k">for</span> <span class="p">(</span><span class="kd">let</span> <span class="nx">item</span> <span class="k">of</span> <span class="nx">data</span><span class="p">[</span><span class="nx">category</span><span class="p">])</span> <span class="p">{</span>
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<span class="kd">let</span> <span class="nx">node</span> <span class="o">=</span> <span class="nx">trie</span><span class="p">.</span><span class="nx">add</span><span class="p">(</span><span class="nx">item</span><span class="p">);</span>
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<span class="nx">node</span><span class="p">.</span><span class="nx">category</span> <span class="o">=</span> <span class="nx">category</span><span class="p">;</span>
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<span class="p">}</span>
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<span class="p">}</span></code></pre></figure>
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<p>As simple as that, our trie is made, it looks like this: <a href="https://mdibaiee.github.io/autocomplete-trie/demo/data.html">Data</a></p>
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<p>Now, let’s actually show results:</p>
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<figure class="highlight"><pre><code class="language-javascript" data-lang="javascript"><span class="kd">const</span> <span class="nx">input</span> <span class="o">=</span> <span class="nb">document</span><span class="p">.</span><span class="nx">querySelector</span><span class="p">(</span><span class="dl">'</span><span class="s1">input</span><span class="dl">'</span><span class="p">);</span>
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<span class="kd">const</span> <span class="nx">results</span> <span class="o">=</span> <span class="nb">document</span><span class="p">.</span><span class="nx">querySelector</span><span class="p">(</span><span class="dl">'</span><span class="s1">#results</span><span class="dl">'</span><span class="p">);</span>
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<span class="nx">input</span><span class="p">.</span><span class="nx">addEventListener</span><span class="p">(</span><span class="dl">'</span><span class="s1">keyup</span><span class="dl">'</span><span class="p">,</span> <span class="p">()</span> <span class="o">=></span> <span class="p">{</span>
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<span class="nx">results</span><span class="p">.</span><span class="nx">innerHTML</span> <span class="o">=</span> <span class="dl">''</span><span class="p">;</span>
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<span class="kd">const</span> <span class="nx">nodes</span> <span class="o">=</span> <span class="nx">trie</span><span class="p">.</span><span class="nx">find</span><span class="p">(</span><span class="nx">input</span><span class="p">.</span><span class="nx">value</span><span class="p">);</span>
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<span class="k">if</span> <span class="p">(</span><span class="o">!</span><span class="nx">nodes</span><span class="p">)</span> <span class="k">return</span><span class="p">;</span>
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<span class="k">for</span> <span class="p">(</span><span class="kd">let</span> <span class="nx">node</span> <span class="k">of</span> <span class="nx">nodes</span><span class="p">.</span><span class="nx">children</span><span class="p">)</span> <span class="p">{</span>
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<span class="kd">const</span> <span class="nx">category</span> <span class="o">=</span> <span class="nx">node</span><span class="p">.</span><span class="nx">category</span> <span class="p">?</span> <span class="s2">`- </span><span class="p">${</span><span class="nx">node</span><span class="p">.</span><span class="nx">category</span><span class="p">}</span><span class="s2">`</span> <span class="p">:</span> <span class="dl">''</span><span class="p">;</span>
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<span class="nx">results</span><span class="p">.</span><span class="nx">innerHTML</span> <span class="o">+=</span> <span class="s2">`<li></span><span class="p">${</span><span class="nx">node</span><span class="p">.</span><span class="nx">value</span><span class="p">}</span><span class="s2"> </span><span class="p">${</span><span class="nx">category</span><span class="p">}</span><span class="s2"></li>`</span><span class="p">;</span>
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<span class="p">}</span>
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<span class="p">});</span></code></pre></figure>
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<p><a href="https://mdibaiee.github.io/autocomplete-trie/1.html">Autocomplete 1</a>
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<img src="/img/autocomplete-1.png" alt="Autocomplete 1" />
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This will only show the instant-childs of the word entered, but that’s not what we want, we want to show <em>complete</em> words, how do we do that?</p>
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<p>First, we need a way to detect complete words, we can have a flag to recognize complete words, we can modify our <code class="language-plaintext highlighter-rouge">add</code> method to
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automatically flag whole words or we can manually add the flag after adding the node, as we did by setting a category for our words,
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so we already have a flag to recognize whole words, that’s our <code class="language-plaintext highlighter-rouge">category</code> property, now let’s add a new method to our Trie class to find
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whole words.</p>
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<figure class="highlight"><pre><code class="language-javascript" data-lang="javascript"><span class="p">...</span>
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<span class="nx">findWords</span><span class="p">(</span><span class="nx">value</span><span class="p">,</span> <span class="nx">parent</span> <span class="o">=</span> <span class="k">this</span><span class="p">.</span><span class="nx">root</span><span class="p">)</span> <span class="p">{</span>
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<span class="kd">let</span> <span class="nx">top</span> <span class="o">=</span> <span class="k">this</span><span class="p">.</span><span class="nx">find</span><span class="p">(</span><span class="nx">value</span><span class="p">,</span> <span class="nx">parent</span><span class="p">);</span>
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<span class="k">if</span> <span class="p">(</span><span class="o">!</span><span class="nx">top</span><span class="p">)</span> <span class="k">return</span> <span class="p">[];</span>
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<span class="kd">let</span> <span class="nx">words</span> <span class="o">=</span> <span class="p">[];</span>
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<span class="nx">top</span><span class="p">.</span><span class="nx">children</span><span class="p">.</span><span class="nx">forEach</span><span class="p">(</span><span class="kd">function</span> <span class="nx">getWords</span><span class="p">(</span><span class="nx">node</span><span class="p">)</span> <span class="p">{</span>
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<span class="k">if</span> <span class="p">(</span><span class="nx">node</span><span class="p">.</span><span class="nx">category</span><span class="p">)</span> <span class="nx">words</span><span class="p">.</span><span class="nx">push</span><span class="p">(</span><span class="nx">node</span><span class="p">);</span>
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<span class="nx">node</span><span class="p">.</span><span class="nx">children</span><span class="p">.</span><span class="nx">forEach</span><span class="p">(</span><span class="nx">getWords</span><span class="p">);</span>
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<span class="p">});</span>
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<span class="k">return</span> <span class="nx">words</span><span class="p">;</span>
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<span class="p">}</span>
|
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<span class="p">...</span></code></pre></figure>
|
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<p>And change our event listener like so:</p>
|
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<figure class="highlight"><pre><code class="language-javascript" data-lang="javascript"><span class="kd">const</span> <span class="nx">input</span> <span class="o">=</span> <span class="nb">document</span><span class="p">.</span><span class="nx">querySelector</span><span class="p">(</span><span class="dl">'</span><span class="s1">input</span><span class="dl">'</span><span class="p">);</span>
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<span class="kd">const</span> <span class="nx">results</span> <span class="o">=</span> <span class="nb">document</span><span class="p">.</span><span class="nx">querySelector</span><span class="p">(</span><span class="dl">'</span><span class="s1">#results</span><span class="dl">'</span><span class="p">);</span>
|
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<span class="nx">input</span><span class="p">.</span><span class="nx">addEventListener</span><span class="p">(</span><span class="dl">'</span><span class="s1">keyup</span><span class="dl">'</span><span class="p">,</span> <span class="p">()</span> <span class="o">=></span> <span class="p">{</span>
|
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|
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<span class="nx">results</span><span class="p">.</span><span class="nx">innerHTML</span> <span class="o">=</span> <span class="dl">''</span><span class="p">;</span>
|
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|
|||
|
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<span class="kd">const</span> <span class="nx">nodes</span> <span class="o">=</span> <span class="nx">trie</span><span class="p">.</span><span class="nx">findWords</span><span class="p">(</span><span class="nx">input</span><span class="p">.</span><span class="nx">value</span><span class="p">);</span> <span class="c1">// << Change</span>
|
|||
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|
|||
|
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<span class="k">if</span> <span class="p">(</span><span class="o">!</span><span class="nx">nodes</span><span class="p">.</span><span class="nx">length</span><span class="p">)</span> <span class="k">return</span><span class="p">;</span> <span class="c1">// << Change</span>
|
|||
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|
|||
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<span class="k">for</span> <span class="p">(</span><span class="kd">let</span> <span class="nx">node</span> <span class="k">of</span> <span class="nx">nodes</span><span class="p">)</span> <span class="p">{</span> <span class="c1">// << Change</span>
|
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|
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<span class="kd">const</span> <span class="nx">category</span> <span class="o">=</span> <span class="nx">node</span><span class="p">.</span><span class="nx">category</span> <span class="p">?</span> <span class="s2">`- </span><span class="p">${</span><span class="nx">node</span><span class="p">.</span><span class="nx">category</span><span class="p">}</span><span class="s2">`</span> <span class="p">:</span> <span class="dl">''</span><span class="p">;</span>
|
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|
|||
|
|
<span class="nx">results</span><span class="p">.</span><span class="nx">innerHTML</span> <span class="o">+=</span> <span class="s2">`<li></span><span class="p">${</span><span class="nx">node</span><span class="p">.</span><span class="nx">value</span><span class="p">}</span><span class="s2"> </span><span class="p">${</span><span class="nx">category</span><span class="p">}</span><span class="s2"></li>`</span><span class="p">;</span>
|
|||
|
|
<span class="p">}</span>
|
|||
|
|
<span class="p">});</span></code></pre></figure>
|
|||
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|
|||
|
|
<p><a href="https://mdibaiee.github.io/autocomplete-trie/2.html">Autocomplete 2</a>
|
|||
|
|
<img src="/img/autocomplete-2.png" alt="Autocomplete 2" />
|
|||
|
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Ta-daa!</p>
|
|||
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|
|||
|
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<p>We have our autocomplete working! Let’s add zsh-like-tab-to-next-char functionality.</p>
|
|||
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|
|||
|
|
<figure class="highlight"><pre><code class="language-javascript" data-lang="javascript"><span class="nx">input</span><span class="p">.</span><span class="nx">addEventListener</span><span class="p">(</span><span class="dl">'</span><span class="s1">keydown</span><span class="dl">'</span><span class="p">,</span> <span class="nx">e</span> <span class="o">=></span> <span class="p">{</span>
|
|||
|
|
<span class="c1">// Tab Key</span>
|
|||
|
|
<span class="k">if</span> <span class="p">(</span><span class="nx">e</span><span class="p">.</span><span class="nx">keyCode</span> <span class="o">===</span> <span class="mi">9</span><span class="p">)</span> <span class="p">{</span>
|
|||
|
|
<span class="nx">e</span><span class="p">.</span><span class="nx">preventDefault</span><span class="p">();</span>
|
|||
|
|
<span class="kd">const</span> <span class="nx">current</span> <span class="o">=</span> <span class="nx">trie</span><span class="p">.</span><span class="nx">find</span><span class="p">(</span><span class="nx">input</span><span class="p">.</span><span class="nx">value</span><span class="p">);</span>
|
|||
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|
|
|||
|
|
<span class="k">if</span> <span class="p">(</span><span class="o">!</span><span class="nx">current</span><span class="p">.</span><span class="nx">children</span><span class="p">.</span><span class="nx">length</span><span class="p">)</span> <span class="k">return</span><span class="p">;</span>
|
|||
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|
|
|||
|
|
<span class="nx">input</span><span class="p">.</span><span class="nx">value</span> <span class="o">=</span> <span class="nx">current</span><span class="p">.</span><span class="nx">children</span><span class="p">[</span><span class="mi">0</span><span class="p">].</span><span class="nx">value</span><span class="p">;</span>
|
|||
|
|
<span class="p">}</span>
|
|||
|
|
<span class="p">});</span></code></pre></figure>
|
|||
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|
|||
|
|
<p>That’s it! We have an input with autocomplete and tab-to-next-char. Isn’t it awesome?</p>
|
|||
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|
|||
|
|
<p><a href="https://mdibaiee.github.io/autocomplete-trie/2.html">Final Result</a></p>
|
|||
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|
|||
|
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<p><em>Pst! I have a repository of algorithm implementations in ES6, you might want to take a look! <a href="https://github.com/mdibaiee/harmony-algorithms">mdibaiee/harmony-algorithms</a></em></p>
|
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</article>
|
|||
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|
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|
<div class="share-page">
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Share in
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<a href="https://plus.google.com/share?url=http://localhost:4000/autocomplete-predict-trie/" rel="nofollow" target="_blank" title="Share on Google+">Google+</a>
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