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| </div><div id='content' class='page-1'><div class='row'><div class='row-fluid'><div class='col-lg-3'><ul class='nav-sidebar'><li><a href='./'>Blog index</a></li><li class='active'><a href='#doc'>Fun with rating stars</a></li><li><a href='#_star_ratings' class='anchor-link'>Star Ratings</a></li><li><a href='#_increasing_robustness' class='anchor-link'>Increasing Robustness</a></li><li><a href='#_references' 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> |
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