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30secondsofcode
2018-10-16 08:30:05 +00:00
parent 3fe8e4ba46
commit 76005943e2
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2
README.md
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@ -1010,7 +1010,7 @@ Use `Array.prototype.reduce()` to create an object, where the keys are produced
```js
const countBy = (arr, fn) =>
arr.map(typeof fn === 'function' ? fn : val => val[fn]).reduce((acc, val, i) => {
arr.map(typeof fn === 'function' ? fn : val => val[fn]).reduce((acc, val) => {
acc[val] = (acc[val] || 0) + 1;
return acc;
}, {});

2
docs/index.html
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@ -118,7 +118,7 @@
</pre></div><div class="card code-card"><div class="corner beginner"></div><div class="section card-content"><h4 id="compact">compact</h4><p>Removes falsey values from an array.</p><p>Use <code>Array.prototype.filter()</code> to filter out falsey values (<code>false</code>, <code>null</code>, <code>0</code>, <code>&quot;&quot;</code>, <code>undefined</code>, and <code>NaN</code>).</p></div><div class="copy-button-container"><button class="copy-button" aria-label="Copy to clipboard"></button></div><pre class="section card-code language-js"><span class="token keyword">const</span> <span class="token function-variable function">compact</span> <span class="token operator">=</span> arr <span class="token operator">=></span> arr<span class="token punctuation">.</span><span class="token function">filter</span><span class="token punctuation">(</span>Boolean<span class="token punctuation">);</span>
</pre><label class="collapse">examples</label><pre class="section card-examples language-js"><span class="token function">compact</span><span class="token punctuation">([</span><span class="token number">0</span><span class="token punctuation">,</span> <span class="token number">1</span><span class="token punctuation">,</span> <span class="token boolean">false</span><span class="token punctuation">,</span> <span class="token number">2</span><span class="token punctuation">,</span> <span class="token string">''</span><span class="token punctuation">,</span> <span class="token number">3</span><span class="token punctuation">,</span> <span class="token string">'a'</span><span class="token punctuation">,</span> <span class="token string">'e'</span> <span class="token operator">*</span> <span class="token number">23</span><span class="token punctuation">,</span> <span class="token number">NaN</span><span class="token punctuation">,</span> <span class="token string">'s'</span><span class="token punctuation">,</span> <span class="token number">34</span><span class="token punctuation">]);</span> <span class="token comment">// [ 1, 2, 3, 'a', 's', 34 ]</span>
</pre></div><div class="card code-card"><div class="corner intermediate"></div><div class="section card-content"><h4 id="countby">countBy</h4><p>Groups the elements of an array based on the given function and returns the count of elements in each group.</p><p>Use <code>Array.prototype.map()</code> to map the values of an array to a function or property name. Use <code>Array.prototype.reduce()</code> to create an object, where the keys are produced from the mapped results.</p></div><div class="copy-button-container"><button class="copy-button" aria-label="Copy to clipboard"></button></div><pre class="section card-code language-js"><span class="token keyword">const</span> <span class="token function-variable function">countBy</span> <span class="token operator">=</span> <span class="token punctuation">(</span>arr<span class="token punctuation">,</span> fn<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><span class="token keyword">typeof</span> fn <span class="token operator">===</span> <span class="token string">'function'</span> <span class="token operator">?</span> fn <span class="token punctuation">:</span> val <span class="token operator">=></span> val<span class="token punctuation">[</span>fn<span class="token punctuation">]).</span><span class="token function">reduce</span><span class="token punctuation">((</span>acc<span class="token punctuation">,</span> val<span class="token punctuation">,</span> i<span class="token punctuation">)</span> <span class="token operator">=></span> <span class="token punctuation">{</span>
arr<span class="token punctuation">.</span><span class="token function">map</span><span class="token punctuation">(</span><span class="token keyword">typeof</span> fn <span class="token operator">===</span> <span class="token string">'function'</span> <span class="token operator">?</span> fn <span class="token punctuation">:</span> val <span class="token operator">=></span> val<span class="token punctuation">[</span>fn<span class="token punctuation">]).</span><span class="token function">reduce</span><span class="token punctuation">((</span>acc<span class="token punctuation">,</span> val<span class="token punctuation">)</span> <span class="token operator">=></span> <span class="token punctuation">{</span>
acc<span class="token punctuation">[</span>val<span class="token punctuation">]</span> <span class="token operator">=</span> <span class="token punctuation">(</span>acc<span class="token punctuation">[</span>val<span class="token punctuation">]</span> <span class="token operator">||</span> <span class="token number">0</span><span class="token punctuation">)</span> <span class="token operator">+</span> <span class="token number">1</span><span class="token punctuation">;</span>
<span class="token keyword">return</span> acc<span class="token punctuation">;
}, {});</span>