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<html lang="en"><head><meta charset="UTF-8"/><meta name="viewport" content="width=device-width, initial-scale=1.0"/><title>One-Hot Encoding · Flux</title><script>(function(i,s,o,g,r,a,m){i['GoogleAnalyticsObject']=r;i[r]=i[r]||function(){
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</script><link href="https://cdnjs.cloudflare.com/ajax/libs/normalize/4.2.0/normalize.min.css" rel="stylesheet" type="text/css"/><link href="https://fonts.googleapis.com/css?family=Lato|Roboto+Mono" rel="stylesheet" type="text/css"/><link href="https://cdnjs.cloudflare.com/ajax/libs/font-awesome/4.6.3/css/font-awesome.min.css" rel="stylesheet" type="text/css"/><link href="https://cdnjs.cloudflare.com/ajax/libs/highlight.js/9.12.0/styles/default.min.css" rel="stylesheet" type="text/css"/><script>documenterBaseURL=".."</script><script src="https://cdnjs.cloudflare.com/ajax/libs/require.js/2.2.0/require.min.js" data-main="../assets/documenter.js"></script><script src="../siteinfo.js"></script><script src="../../versions.js"></script><link href="../assets/documenter.css" rel="stylesheet" type="text/css"/><link href="../../flux.css" rel="stylesheet" type="text/css"/></head><body><nav class="toc"><h1>Flux</h1><select id="version-selector" onChange="window.location.href=this.value" style="visibility: hidden"></select><form class="search" action="../search.html"><input id="search-query" name="q" type="text" placeholder="Search docs"/></form><ul><li><a class="toctext" href="../index.html">Home</a></li><li><span class="toctext">Building Models</span><ul><li><a class="toctext" href="../models/basics.html">Basics</a></li><li><a class="toctext" href="../models/recurrence.html">Recurrence</a></li><li><a class="toctext" href="../models/layers.html">Layer Reference</a></li></ul></li><li><span class="toctext">Training Models</span><ul><li><a class="toctext" href="../training/optimisers.html">Optimisers</a></li><li><a class="toctext" href="../training/training.html">Training</a></li></ul></li><li class="current"><a class="toctext" href="onehot.html">One-Hot Encoding</a><ul class="internal"><li><a class="toctext" href="#Batches-1">Batches</a></li></ul></li><li><a class="toctext" href="../gpu.html">GPU Support</a></li><li><a class="toctext" href="../contributing.html">Contributing & Help</a></li></ul></nav><article id="docs"><header><nav><ul><li><a href="onehot.html">One-Hot Encoding</a></li></ul><a class="edit-page" href="https://github.com/FluxML/Flux.jl/tree/d3419c943bd8c8c3d06ffa8ea5618625b3b14613/docs/src/data/onehot.md"><span class="fa"></span> Edit on GitHub</a></nav><hr/><div id="topbar"><span>One-Hot Encoding</span><a class="fa fa-bars" href="#"></a></div></header><h1><a class="nav-anchor" id="One-Hot-Encoding-1" href="#One-Hot-Encoding-1">One-Hot Encoding</a></h1><p>It's common to encode categorical variables (like <code>true</code>, <code>false</code> or <code>cat</code>, <code>dog</code>) in "one-of-k" or <a href="https://en.wikipedia.org/wiki/One-hot">"one-hot"</a> form. Flux provides the <code>onehot</code> function to make this easy.</p><pre><code class="language-none">julia> using Flux: onehot
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julia> onehot(:b, [:a, :b, :c])
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3-element Flux.OneHotVector:
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false
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true
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false
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julia> onehot(:c, [:a, :b, :c])
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3-element Flux.OneHotVector:
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false
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false
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true</code></pre><p>The inverse is <code>argmax</code> (which can take a general probability distribution, as well as just booleans).</p><pre><code class="language-julia">julia> argmax(ans, [:a, :b, :c])
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:c
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julia> argmax([true, false, false], [:a, :b, :c])
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:a
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julia> argmax([0.3, 0.2, 0.5], [:a, :b, :c])
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:c</code></pre><h2><a class="nav-anchor" id="Batches-1" href="#Batches-1">Batches</a></h2><p><code>onehotbatch</code> creates a batch (matrix) of one-hot vectors, and <code>argmax</code> treats matrices as batches.</p><pre><code class="language-julia">julia> using Flux: onehotbatch
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julia> onehotbatch([:b, :a, :b], [:a, :b, :c])
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3×3 Flux.OneHotMatrix:
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false true false
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true false true
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false false false
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julia> onecold(ans, [:a, :b, :c])
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3-element Array{Symbol,1}:
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:b
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:a
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:b</code></pre><p>Note that these operations returned <code>OneHotVector</code> and <code>OneHotMatrix</code> rather than <code>Array</code>s. <code>OneHotVector</code>s behave like normal vectors but avoid any unnecessary cost compared to using an integer index directly. For example, multiplying a matrix with a one-hot vector simply slices out the relevant row of the matrix under the hood.</p><footer><hr/><a class="previous" href="../training/training.html"><span class="direction">Previous</span><span class="title">Training</span></a><a class="next" href="../gpu.html"><span class="direction">Next</span><span class="title">GPU Support</span></a></footer></article></body></html>
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