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[Tut] 5 Effective Methods to Sort a List of String Numbers Numerically in Python - xSicKxBot - 08-16-2023
[Tut] 5 Effective Methods to Sort a List of String Numbers Numerically in Python
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<div class="kksr-legend" style="font-size: 19.2px;"> 5/5 – (1 vote) </div>
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<h2 class="wp-block-heading">Problem Formulation</h2>
<p>Sorting a list of string numbers numerically in Python can lead to unexpected issues. </p>
<p>For <a rel="noreferrer noopener" href="https://stackoverflow.com/questions/3426108/how-to-sort-a-list-of-strings-numerically" data-type="URL" data-id="https://stackoverflow.com/questions/3426108/how-to-sort-a-list-of-strings-numerically" target="_blank">example</a>, using the naive approach to sort the list <code>lst = ["1", "10", "3", "22", "23", "4", "2", "200"]</code> using <code>lst.sort()</code> will result in the incorrect order as it sorts the list of strings lexicographically, not numerically.</p>
<p>In this short article, my goal is to present the <strong>five best methods to correctly sort this list numerically</strong>. My recommended approach is the fifth one, see below. <img decoding="async" src="https://s.w.org/images/core/emoji/14.0.0/72x72/1f447.png" alt="?" class="wp-smiley" style="height: 1em; max-height: 1em;" /></p>
<h2 class="wp-block-heading">Method 1: Convert Strings to Integers and Sort</h2>
<p>This method involves converting each string in the list to an integer and then sorting them. It’s a direct and simple approach to ensure numerical ordering.</p>
<pre class="EnlighterJSRAW" data-enlighter-language="generic" data-enlighter-theme="" data-enlighter-highlight="" data-enlighter-linenumbers="" data-enlighter-lineoffset="" data-enlighter-title="" data-enlighter-group="">lst = [int(x) for x in lst]
lst.sort()
</pre>
<p><strong>Output</strong>: <code>['1', '2', '3', '4', '10', '22', '23', '200']</code></p>
<p><img decoding="async" src="https://s.w.org/images/core/emoji/14.0.0/72x72/1f4a1.png" alt="?" class="wp-smiley" style="height: 1em; max-height: 1em;" /> <strong>Recommended</strong>: <a href="https://blog.finxter.com/list-comprehension/" data-type="post" data-id="1171" target="_blank" rel="noreferrer noopener">Python List Comprehension</a></p>
<h2 class="wp-block-heading">Method 2: Using the <code>key</code> Parameter with sort()</h2>
<p>This method uses the <code>key</code> parameter with the <code>int</code> function to sort the strings as integers. It allows for numerical comparison without altering the original strings.</p>
<pre class="EnlighterJSRAW" data-enlighter-language="generic" data-enlighter-theme="" data-enlighter-highlight="" data-enlighter-linenumbers="" data-enlighter-lineoffset="" data-enlighter-title="" data-enlighter-group="">lst.sort(key=int)
</pre>
<p><strong>Output</strong>: <code>['1', '2', '3', '4', '10', '22', '23', '200']</code></p>
<p><img decoding="async" src="https://s.w.org/images/core/emoji/14.0.0/72x72/1f4a1.png" alt="?" class="wp-smiley" style="height: 1em; max-height: 1em;" /> <strong>Recommended</strong>: <a href="https://blog.finxter.com/sort-a-list-string-tuple-in-python-sort-sorted/" data-type="post" data-id="1550507" target="_blank" rel="noreferrer noopener">Python <code>list.sort()</code> with key parameter</a></p>
<h2 class="wp-block-heading">Method 3: Using the natsort Module</h2>
<p>The <code>natsort</code> module provides a natural sorting algorithm, useful for sorting strings that represent numbers. This method can handle more complex string sorting scenarios.</p>
<pre class="EnlighterJSRAW" data-enlighter-language="generic" data-enlighter-theme="" data-enlighter-highlight="" data-enlighter-linenumbers="" data-enlighter-lineoffset="" data-enlighter-title="" data-enlighter-group="">from natsort import natsorted
lst = natsorted(lst)
</pre>
<p><strong>Output</strong>: <code>['1', '2', '3', '4', '10', '22', '23', '200']</code></p>
<h2 class="wp-block-heading">Method 4: Using Regular Expressions</h2>
<p>Using regular expressions, this method can sort strings containing both letters and numbers. It converts the numeric parts into floats for comparison, handling mixed content.</p>
<pre class="EnlighterJSRAW" data-enlighter-language="generic" data-enlighter-theme="" data-enlighter-highlight="" data-enlighter-linenumbers="" data-enlighter-lineoffset="" data-enlighter-title="" data-enlighter-group="">import re def sort_human(l): convert = lambda text: float(text) if text.isdigit() else text alphanum = lambda key: [convert© for c in re.split('([-+]?[0-9]*\.?[0-9]*)', key)] l.sort(key=alphanum) return l lst = sort_human(lst)
</pre>
<p><strong>Output</strong>: <code>['1', '2', '3', '4', '10', '22', '23', '200']</code></p>
<p><img decoding="async" src="https://s.w.org/images/core/emoji/14.0.0/72x72/1f4a1.png" alt="?" class="wp-smiley" style="height: 1em; max-height: 1em;" /> <strong>Recommended</strong>: <a href="https://blog.finxter.com/python-regex/" target="_blank" rel="noreferrer noopener">Python Regular Expression Superpower</a></p>
<h2 class="wp-block-heading">Method 5: Using sorted() with key Parameter (Recommended)</h2>
<p>This method combines the simplicity of using the <code>key</code> parameter with the benefit of creating a new sorted list, leaving the original untouched. It’s concise and effective.</p>
<pre class="EnlighterJSRAW" data-enlighter-language="generic" data-enlighter-theme="" data-enlighter-highlight="" data-enlighter-linenumbers="" data-enlighter-lineoffset="" data-enlighter-title="" data-enlighter-group="">lst = sorted(lst, key=int)
</pre>
<p><strong>Output</strong>: <code>['1', '2', '3', '4', '10', '22', '23', '200']</code></p>
<p><img decoding="async" src="https://s.w.org/images/core/emoji/14.0.0/72x72/1f4a1.png" alt="?" class="wp-smiley" style="height: 1em; max-height: 1em;" /> <strong>Recommended</strong>: <a href="https://blog.finxter.com/python-sorted-function/" data-type="post" data-id="18072" target="_blank" rel="noreferrer noopener">Python <code>sorted()</code> function</a></p>
<h2 class="wp-block-heading">Summary – When to Use Which</h2>
<ul class="has-global-color-8-background-color has-background">
<li><strong>Method 1</strong>: Converts strings to integers, then sorts. Simple but alters the original list.</li>
<li><strong>Method 2</strong>: Uses the <code>key</code> parameter with <code>int</code> for sorting. Preserves the original strings.</li>
<li><strong>Method 3</strong>: Utilizes the <code>natsort</code> module. Handles complex scenarios.</li>
<li><strong>Method 4</strong>: Employs regular expressions for sorting alphanumeric strings.</li>
<li><strong>Method 5 (Recommended)</strong>: Combines the simplicity of using <code>key</code> with <code>sorted()</code>. Preserves the original list and offers concise code.</li>
</ul>
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