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[Tut] How to Sort a List Alphabetically in Python? - xSicKxBot - 03-31-2020
How to Sort a List Alphabetically in Python?
<div><p><strong>Problem</strong>: Given a list of strings. Sort the list of strings in alphabetical order.</p>
<p><strong>Example: </strong></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="">['Frank', 'Alice', 'Bob'] --> ['Alice', 'Bob', 'Frank']</pre>
<p><strong>Solution</strong>: Use the <a rel="noreferrer noopener" href="https://blog.finxter.com/python-list-sort/" target="_blank">list.sort()</a> method without argument to solve the list in lexicographical order which is a generalization of alphabetical order (also applies to the second, third, … characters). </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 = ['Frank', 'Alice', 'Bob']
lst.sort()
print(lst)
# ['Alice', 'Bob', 'Frank']</pre>
<p><strong>Try It Yourself:</strong></p>
<figure class="wp-block-embed-wordpress wp-block-embed is-type-wp-embed is-provider-repl-it">
<div class="wp-block-embed__wrapper">
<iframe title="sortalphabet" class="wp-embedded-content" sandbox="allow-scripts" security="restricted" src="https://repl.it/@finxter/sortalphabet?lite=true#?secret=HiPAailwCE" data-secret="HiPAailwCE" width="800" height="600" frameborder="0"></iframe>
</div>
</figure>
<h2>Python List Sort Alphabetically Case Insensitive</h2>
<p>The problem with the default list.sort() or sorted(list) method is that they consider capitalization. This way, it can lead to strange sortings like this:</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 = ['ab', 'Ac', 'ad']
lst.sort()
print(lst)
# ['Ac', 'ab', 'ad']</pre>
<p>Intuitively, you would expect the string <code>'ab'</code> to occur before <code>'Ac'</code>, right?</p>
<p>To ignore the capitalization, you can simply call the <code>x.lower()</code> method on each element <code>x</code> before sorting the list. </p>
<p>However, my preferred method is to use the key argument to accomplish the same thing in a single line of code:</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 = ['ab', 'Ac', 'ad']
lst.sort(key=lambda x: x.lower())
print(lst)
# ['ab', 'Ac', 'ad']</pre>
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<h2>Python List Sort Alphabetically Reverse</h2>
<p>You can reverse the order of the list by using the reverse keyword. Set <code>reverse=False</code> to sort in ascending order and set <code>reverse=True</code> to sort in descending order. </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 = ['Frank', 'Alice', 'Bob'] lst.sort(reverse=False)
print(lst)
# ['Alice', 'Bob', 'Frank'] lst.sort(reverse=True)
print(lst)
# ['Frank', 'Bob', 'Alice']</pre>
<h2>Python List Sort Alphabetically and Numerically</h2>
<p><strong>Problem</strong>: You’ve got a list of strings. Each strings contains a number. You want the numbers to sort numerically (e.g. 100 comes <em>after </em>20, not before) but the characters to sort alphabetically (e.g., <code>'c'</code> comes before <code>'d'</code>).</p>
<p><strong>Example</strong>:</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="">['alice 100', 'alice 20', 'bob 99'] --> ['alice 20', 'alice 100', 'bob 99'</pre>
<p><strong>Naive Solution (doesn’t work):</strong> Use the list.sort() method to sort the list alphabetically:</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 = ['alice 100', 'alice 20', 'bob 99']
lst.sort()
print(lst)
# ['alice 100', 'alice 20', 'bob 99']</pre>
<p>Because the number 100 comes before 20 in an alphabetical order, the string <code>'alice 100'</code> is placed before <code>'alice 20'</code>.</p>
<p><strong>Solution</strong>: I found <a href="https://stackoverflow.com/questions/2669059/how-to-sort-alpha-numeric-set-in-python" target="_blank" rel="noreferrer noopener">this</a> code on StackOverflow that nicely demonstrates how to do this:</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 sorted_nicely(l): """ Sort the given iterable in the way that humans expect.""" convert = lambda text: int(text) if text.isdigit() else text alphanum_key = lambda key: [convert© for c in re.split('([0-9]+)', key)] l.sort(key = alphanum_key) lst = ['alice 100', 'alice 20', 'bob 99']
sorted_nicely(lst)
print(lst)
# ['alice 20', 'alice 100', 'bob 99']</pre>
<p>The idea is to differentiate characters and numbers and use them as the basis of comparison for the sort routine.</p>
<h2>Where to Go From Here?</h2>
<p><em>The <code>list.sort()</code> method sorts the list elements in place in an ascending manner. To customize the default sorting behavior, use the optional <code>key</code> argument by passing a function that returns a comparable value for each element in the list. With the optional Boolean <code>reverse</code> argument, you can switch from ascending (<code>reverse=False</code>) to descending order (<code>reverse=True</code>).</em></p>
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