blog/fun-with-rating-stars.html

<!DOCTYPE html>     <html class="no-js"> <head> <meta charset='utf-8'/><meta http-equiv='X-UA-Compatible' content='IE=edge'/><meta name='viewport' content='width=device-width, initial-scale=1'/><meta name='keywords' content='groovy'/><meta name='description' content='Inspired by a recent tweet, this blog looks at producing a string of stars corresponding to a rating.'/><title>The Apache Groovy programming language - Blogs - Fun with rating stars</title><link href='../img/favicon.ico' type='image/x-ico' rel='icon'/><link rel='stylesheet' type='text/css' href='../css/bootstrap.css'/><link rel='stylesheet' type='text/css' href='../css/font-awesome.min.css'/><link rel='stylesheet' type='text/css' href='../css/style.css'/><link rel='stylesheet' type='text/css' href='https://cdnjs.cloudflare.com/ajax/libs/prettify/r298/prettify.min.css'/> </head><body> <div id='fork-me'> <a href='https://github.com/apache/groovy'> <img style='position: fixed; top: 20px; right: -58px; border: 0; z-index: 100; 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class='anchor-link'>References</a></li></ul></div><div class='col-lg-8 col-lg-pull-0'><a name='doc'></a><h1>Fun with rating stars</h1><p><span>Author: <i>Paul King</i></span><br/><span>Published: 2023-01-25 12:00AM</span></p><hr/><div class="sect1"> <h2 id="_star_ratings">Star Ratings</h2> <div class="sectionbody"> <div class="paragraph"> <p>A recent tweet showed some C# code for producing a String of stars that might be used when displaying ratings on a website:</p> </div> <div class="paragraph"> <p><span class="image"><img src="img/star_ratings_csharp.png" alt="Image of original tweet" width="366"></span></p> </div> <div class="paragraph"> <p>Let’s have a look at several ways to do the same thing in Groovy.</p> </div> <div class="listingblock"> <div class="content"> <pre class="prettyprint highlight"><code>def rating0(percentage) { int stars = Math.ceil(percentage * 10) ("🔵" * stars).padRight(10, "⚪") }</code></pre> </div> </div> <div class="listingblock"> <div class="content"> <pre class="prettyprint highlight"><code>def rating1(percentage) { int stars = Math.ceil(percentage * 10) "🔵" * stars + "⚪" * (10-stars) }</code></pre> </div> </div> <div class="listingblock"> <div class="content"> <pre class="prettyprint highlight"><code>def rating2(percentage) { int skip = 10 - Math.ceil(percentage * 10) "🔵🔵🔵🔵🔵🔵🔵🔵🔵🔵⚪⚪⚪⚪⚪⚪⚪⚪⚪⚪"[skip..<10+skip] }</code></pre> </div> </div> <div class="listingblock"> <div class="content"> <pre class="prettyprint highlight"><code>def rating3(percentage) { switch(percentage) { case 0 -> "⚪⚪⚪⚪⚪⚪⚪⚪⚪⚪" case { it <= 0.1 } -> "🔵⚪⚪⚪⚪⚪⚪⚪⚪⚪" case { it <= 0.2 } -> "🔵🔵⚪⚪⚪⚪⚪⚪⚪⚪" case { it <= 0.3 } -> "🔵🔵🔵⚪⚪⚪⚪⚪⚪⚪" case { it <= 0.4 } -> "🔵🔵🔵🔵⚪⚪⚪⚪⚪⚪" case { it <= 0.5 } -> "🔵🔵🔵🔵🔵⚪⚪⚪⚪⚪" case { it <= 0.6 } -> "🔵🔵🔵🔵🔵🔵⚪⚪⚪⚪" case { it <= 0.7 } -> "🔵🔵🔵🔵🔵🔵🔵⚪⚪⚪" case { it <= 0.8 } -> "🔵🔵🔵🔵🔵🔵🔵🔵⚪⚪" case { it <= 0.9 } -> "🔵🔵🔵🔵🔵🔵🔵🔵🔵⚪" default -> "🔵🔵🔵🔵🔵🔵🔵🔵🔵🔵" } }</code></pre> </div> </div> <div class="paragraph"> <p>If you want you can test the various edge cases:</p> </div> <div class="listingblock"> <div class="content"> <pre class="prettyprint highlight"><code>for (i in 0..3) for (j in [0, 0.09, 0.1, 0.11, 0.9, 1]) println "rating$i"(j)</code></pre> </div> </div> </div> </div> <div class="sect1"> <h2 id="_increasing_robustness">Increasing Robustness</h2> <div class="sectionbody"> <div class="paragraph"> <p>The code examples here assume that the input is in the range <code>0 <= percentage <= 1</code>. There are several tweaks we could do to guard against inputs outside those ranges.</p> </div> <div class="paragraph"> <p>We could simply add an assert, e.g.:</p> </div> <div class="listingblock"> <div class="content"> <pre class="prettyprint highlight"><code>def rating0b(percentage) { assert percentage >= 0 && percentage <= 1 int stars = Math.ceil(percentage * 10) ("🔵" * stars).padRight(10, "⚪") }</code></pre> </div> </div> <div class="paragraph"> <p>Or, if we wanted to not fail, tweak some of our conditions, e.g. for <code>rating3</code>, instead of <code>case 0</code>, we could use <code>case { it ⇐ 0 }</code>.</p> </div> <div class="paragraph"> <p>We could push the checks into our types by making a special class, <code>Percent</code> say, which only permitted the allowed values:</p> </div> <div class="listingblock"> <div class="content"> <pre class="prettyprint highlight"><code>final class Percent { final Double value Percent(Double value) { assert value >= 0 && value <= 1 this.value = value } }</code></pre> </div> </div> <div class="paragraph"> <p>And we could optionally also use some metaprogramming to provide a custom <code>isCase</code> method:</p> </div> <div class="listingblock"> <div class="content"> <pre class="prettyprint highlight"><code>Double.metaClass.isCase = { Percent p -> delegate >= p.value }</code></pre> </div> </div> <div class="paragraph"> <p>Which means we could tweak the rating method to be:</p> </div> <div class="listingblock"> <div class="content"> <pre class="prettyprint highlight"><code>def rating3b(Percent p) { switch(p) { case 0.0d -> "⚪⚪⚪⚪⚪⚪⚪⚪⚪⚪" case 0.1d -> "🔵⚪⚪⚪⚪⚪⚪⚪⚪⚪" case 0.2d -> "🔵🔵⚪⚪⚪⚪⚪⚪⚪⚪" case 0.3d -> "🔵🔵🔵⚪⚪⚪⚪⚪⚪⚪" case 0.4d -> "🔵🔵🔵🔵⚪⚪⚪⚪⚪⚪" case 0.5d -> "🔵🔵🔵🔵🔵⚪⚪⚪⚪⚪" case 0.6d -> "🔵🔵🔵🔵🔵🔵⚪⚪⚪⚪" case 0.7d -> "🔵🔵🔵🔵🔵🔵🔵⚪⚪⚪" case 0.8d -> "🔵🔵🔵🔵🔵🔵🔵🔵⚪⚪" case 0.9d -> "🔵🔵🔵🔵🔵🔵🔵🔵🔵⚪" default -> "🔵🔵🔵🔵🔵🔵🔵🔵🔵🔵" } }</code></pre> </div> </div> <div class="paragraph"> <p>We can be fancier here using <code>@EqualsAndHashCode</code> on the <code>Percent</code> class and/or using <code>@Delegate</code> on the <code>value</code> property, depending on how rich in functionality we wanted the <code>Percent</code> instances to be.</p> </div> <div class="paragraph"> <p>Alternatively, we could use a design-by-contract approach:</p> </div> <div class="listingblock"> <div class="content"> <pre class="prettyprint highlight"><code>@Requires({ percentage >= 0 && percentage <= 1 }) def rating1b(percentage) { int stars = Math.ceil(percentage * 10) "🔵" * stars + "⚪" * (10-stars) }</code></pre> </div> </div> </div> </div> <div class="sect1"> <h2 id="_references">References</h2> <div class="sectionbody"> <div class="paragraph"> <p><a href="https://twitter.com/JeroenFrijters/status/1615204074588180481">Original tweet</a></p> </div> </div> </div></div></div></div></div><footer id='footer'> <div class='row'> <div class='colset-3-footer'> <div class='col-1'> <h1>Groovy</h1><ul> <li><a 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