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30secondsofcode
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@ -105,7 +105,7 @@
}, {});</span>
</pre><label class="collapse">Show examples</label><pre class="language-js"><span class="token function">countBy</span><span class="token punctuation">([</span><span class="token number">6.1</span><span class="token punctuation">,</span> <span class="token number">4.2</span><span class="token punctuation">,</span> <span class="token number">6.3</span><span class="token punctuation">],</span> Math<span class="token punctuation">.</span>floor<span class="token punctuation">);</span> <span class="token comment">// {4: 1, 6: 2}</span>
<span class="token function">countBy</span><span class="token punctuation">([</span><span class="token string">'one'</span><span class="token punctuation">,</span> <span class="token string">'two'</span><span class="token punctuation">,</span> <span class="token string">'three'</span><span class="token punctuation">],</span> <span class="token string">'length'</span><span class="token punctuation">);</span> <span class="token comment">// {3: 2, 5: 1}</span>
</pre><button class="primary clipboard-copy">&#128203;&nbsp;Copy to clipboard</button></div></div><div class="card fluid"><h3 id="countoccurrences" class="section double-padded">countOccurrences</h3><div class="section double-padded"><p>Counts the occurrences of a value in an array.</p><p>Use <code>Array.reduce()</code> to increment a counter each time you encounter the specific value inside the array.</p><pre class="language-js"><span class="token keyword">const</span> <span class="token function-variable function">countOccurrences</span> <span class="token operator">=</span> <span class="token punctuation">(</span>arr<span class="token punctuation">,</span> val<span class="token punctuation">)</span> <span class="token operator">=></span> arr<span class="token punctuation">.</span><span class="token function">reduce</span><span class="token punctuation">((</span>a<span class="token punctuation">,</span> v<span class="token punctuation">)</span> <span class="token operator">=></span> <span class="token punctuation">(</span>v <span class="token operator">===</span> val <span class="token operator">?</span> a <span class="token operator">+</span> <span class="token number">1</span> <span class="token punctuation">:</span> a <span class="token operator">+</span> <span class="token number">0</span><span class="token punctuation">),</span> <span class="token number">0</span><span class="token punctuation">);</span>
</pre><button class="primary clipboard-copy">&#128203;&nbsp;Copy to clipboard</button></div></div><div class="card fluid"><h3 id="countoccurrences" class="section double-padded">countOccurrences</h3><div class="section double-padded"><p>Counts the occurrences of a value in an array.</p><p>Use <code>Array.reduce()</code> to increment a counter each time you encounter the specific value inside the array.</p><pre class="language-js"><span class="token keyword">const</span> <span class="token function-variable function">countOccurrences</span> <span class="token operator">=</span> <span class="token punctuation">(</span>arr<span class="token punctuation">,</span> val<span class="token punctuation">)</span> <span class="token operator">=></span> arr<span class="token punctuation">.</span><span class="token function">reduce</span><span class="token punctuation">((</span>a<span class="token punctuation">,</span> v<span class="token punctuation">)</span> <span class="token operator">=></span> <span class="token punctuation">(</span>v <span class="token operator">===</span> val <span class="token operator">?</span> a <span class="token operator">+</span> <span class="token number">1</span> <span class="token punctuation">:</span> a<span class="token punctuation">),</span> <span class="token number">0</span><span class="token punctuation">);</span>
</pre><label class="collapse">Show examples</label><pre class="language-js"><span class="token function">countOccurrences</span><span class="token punctuation">([</span><span class="token number">1</span><span class="token punctuation">,</span> <span class="token number">1</span><span class="token punctuation">,</span> <span class="token number">2</span><span class="token punctuation">,</span> <span class="token number">1</span><span class="token punctuation">,</span> <span class="token number">2</span><span class="token punctuation">,</span> <span class="token number">3</span><span class="token punctuation">],</span> <span class="token number">1</span><span class="token punctuation">);</span> <span class="token comment">// 3</span>
</pre><button class="primary clipboard-copy">&#128203;&nbsp;Copy to clipboard</button></div></div><div class="card fluid"><h3 id="deepflatten" class="section double-padded">deepFlatten</h3><div class="section double-padded"><p>Deep flattens an array.</p><p>Use recursion. Use <code>Array.concat()</code> with an empty array (<code>[]</code>) and the spread operator (<code>...</code>) to flatten an array. Recursively flatten each element that is an array.</p><pre class="language-js"><span class="token keyword">const</span> <span class="token function-variable function">deepFlatten</span> <span class="token operator">=</span> arr <span class="token operator">=></span> <span class="token punctuation">[].</span><span class="token function">concat</span><span class="token punctuation">(</span><span class="token operator">...</span>arr<span class="token punctuation">.</span><span class="token function">map</span><span class="token punctuation">(</span>v <span class="token operator">=></span> <span class="token punctuation">(</span>Array<span class="token punctuation">.</span><span class="token function">isArray</span><span class="token punctuation">(</span>v<span class="token punctuation">)</span> <span class="token operator">?</span> <span class="token function">deepFlatten</span><span class="token punctuation">(</span>v<span class="token punctuation">) :</span> v<span class="token punctuation">)));</span>
</pre><label class="collapse">Show examples</label><pre class="language-js"><span class="token function">deepFlatten</span><span class="token punctuation">([</span><span class="token number">1</span><span class="token punctuation">, [</span><span class="token number">2</span><span class="token punctuation">], [[</span><span class="token number">3</span><span class="token punctuation">],</span> <span class="token number">4</span><span class="token punctuation">],</span> <span class="token number">5</span><span class="token punctuation">]);</span> <span class="token comment">// [1,2,3,4,5]</span>