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<!-- Generated by pkgdown: do not edit by hand --><html lang="en"><head><meta http-equiv="Content-Type" content="text/html; charset=UTF-8"><meta charset="utf-8"><meta http-equiv="X-UA-Compatible" content="IE=edge"><meta name="viewport" content="width=device-width, initial-scale=1.0"><title>Freeze a reactive value — freezeReactiveVal • shiny</title><!-- favicons --><link rel="icon" type="image/png" sizes="16x16" href="../favicon-16x16.png"><link rel="icon" type="image/png" sizes="32x32" href="../favicon-32x32.png"><link rel="apple-touch-icon" type="image/png" sizes="180x180" href="../apple-touch-icon.png"><link rel="apple-touch-icon" type="image/png" sizes="120x120" href="../apple-touch-icon-120x120.png"><link rel="apple-touch-icon" type="image/png" sizes="76x76" href="../apple-touch-icon-76x76.png"><link rel="apple-touch-icon" type="image/png" sizes="60x60" href="../apple-touch-icon-60x60.png"><!-- jquery --><script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.4.1/jquery.min.js" integrity="sha256-CSXorXvZcTkaix6Yvo6HppcZGetbYMGWSFlBw8HfCJo=" crossorigin="anonymous"></script><!-- Bootstrap --><link rel="stylesheet" href="https://cdnjs.cloudflare.com/ajax/libs/twitter-bootstrap/3.4.1/css/bootstrap.min.css" integrity="sha256-bZLfwXAP04zRMK2BjiO8iu9pf4FbLqX6zitd+tIvLhE=" crossorigin="anonymous"><script src="https://cdnjs.cloudflare.com/ajax/libs/twitter-bootstrap/3.4.1/js/bootstrap.min.js" integrity="sha256-nuL8/2cJ5NDSSwnKD8VqreErSWHtnEP9E7AySL+1ev4=" crossorigin="anonymous"></script><!-- bootstrap-toc --><link rel="stylesheet" href="../bootstrap-toc.css"><script src="../bootstrap-toc.js"></script><!-- Font Awesome icons --><link rel="stylesheet" href="https://cdnjs.cloudflare.com/ajax/libs/font-awesome/5.12.1/css/all.min.css" integrity="sha256-mmgLkCYLUQbXn0B1SRqzHar6dCnv9oZFPEC1g1cwlkk=" crossorigin="anonymous"><link rel="stylesheet" href="https://cdnjs.cloudflare.com/ajax/libs/font-awesome/5.12.1/css/v4-shims.min.css" integrity="sha256-wZjR52fzng1pJHwx4aV2AO3yyTOXrcDW7jBpJtTwVxw=" crossorigin="anonymous"><!-- clipboard.js --><script src="https://cdnjs.cloudflare.com/ajax/libs/clipboard.js/2.0.6/clipboard.min.js" integrity="sha256-inc5kl9MA1hkeYUt+EC3BhlIgyp/2jDIyBLS6k3UxPI=" crossorigin="anonymous"></script><!-- headroom.js --><script src="https://cdnjs.cloudflare.com/ajax/libs/headroom/0.11.0/headroom.min.js" integrity="sha256-AsUX4SJE1+yuDu5+mAVzJbuYNPHj/WroHuZ8Ir/CkE0=" crossorigin="anonymous"></script><script src="https://cdnjs.cloudflare.com/ajax/libs/headroom/0.11.0/jQuery.headroom.min.js" integrity="sha256-ZX/yNShbjqsohH1k95liqY9Gd8uOiE1S4vZc+9KQ1K4=" crossorigin="anonymous"></script><!-- pkgdown --><link href="../pkgdown.css" rel="stylesheet"><script src="../pkgdown.js"></script><meta property="og:title" content="Freeze a reactive value — freezeReactiveVal"><meta property="og:description" content='These functions freeze a reactiveVal(), or an element of a
reactiveValues(). If the value is accessed while frozen, a
"silent" exception is raised and the operation is stopped. This is the same
thing that happens if req(FALSE) is called. The value is thawed
(un-frozen; accessing it will no longer raise an exception) when the current
reactive domain is flushed. In a Shiny application, this occurs after all of
the observers are executed. NOTE: We are considering deprecating
freezeReactiveVal, and freezeReactiveValue except when x is input.
If this affects your app, please let us know by leaving a comment on
this GitHub issue.'><meta property="og:image" content="/logo.png"><!-- mathjax --><script src="https://cdnjs.cloudflare.com/ajax/libs/mathjax/2.7.5/MathJax.js" integrity="sha256-nvJJv9wWKEm88qvoQl9ekL2J+k/RWIsaSScxxlsrv8k=" crossorigin="anonymous"></script><script src="https://cdnjs.cloudflare.com/ajax/libs/mathjax/2.7.5/config/TeX-AMS-MML_HTMLorMML.js" integrity="sha256-84DKXVJXs0/F8OTMzX4UR909+jtl4G7SPypPavF+GfA=" crossorigin="anonymous"></script><!--[if lt IE 9]>
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<h1>Freeze a reactive value</h1>
<small class="dont-index">Source: <a href="https://github.com/rstudio/shiny/blob/HEAD/R/reactives.R" class="external-link"><code>R/reactives.R</code></a></small>
<div class="hidden name"><code>freezeReactiveValue.Rd</code></div>
</div>
<div class="ref-description">
<p>These functions freeze a <code><a href="reactiveVal.html">reactiveVal()</a></code>, or an element of a
<code><a href="reactiveValues.html">reactiveValues()</a></code>. If the value is accessed while frozen, a
"silent" exception is raised and the operation is stopped. This is the same
thing that happens if <code>req(FALSE)</code> is called. The value is thawed
(un-frozen; accessing it will no longer raise an exception) when the current
reactive domain is flushed. In a Shiny application, this occurs after all of
the observers are executed. <strong>NOTE:</strong> We are considering deprecating
<code>freezeReactiveVal</code>, and <code>freezeReactiveValue</code> except when <code>x</code> is <code>input</code>.
If this affects your app, please let us know by leaving a comment on
<a href="https://github.com/rstudio/shiny/issues/3063" class="external-link">this GitHub issue</a>.</p>
</div>
<div id="ref-usage">
<div class="sourceCode"><pre class="sourceCode r"><code><span><span class="fu">freezeReactiveVal</span><span class="op">(</span><span class="va">x</span><span class="op">)</span></span>
<span></span>
<span><span class="fu">freezeReactiveValue</span><span class="op">(</span><span class="va">x</span>, <span class="va">name</span><span class="op">)</span></span></code></pre></div>
</div>
<div id="arguments">
<h2>Arguments</h2>
<dl><dt>x</dt>
<dd><p>For <code>freezeReactiveValue</code>, a <code><a href="reactiveValues.html">reactiveValues()</a></code>
object (like <code>input</code>); for <code>freezeReactiveVal</code>, a
<code><a href="reactiveVal.html">reactiveVal()</a></code> object.</p></dd>
<dt>name</dt>
<dd><p>The name of a value in the <code><a href="reactiveValues.html">reactiveValues()</a></code> object.</p></dd>
</dl></div>
<div id="see-also">
<h2>See also</h2>
<div class="dont-index"><p><code><a href="req.html">req()</a></code></p></div>
</div>
<div id="ref-examples">
<h2>Examples</h2>
<div class="sourceCode"><pre class="sourceCode r"><code><span class="r-in"><span><span class="co">## Only run this examples in interactive R sessions</span></span></span>
<span class="r-in"><span><span class="kw">if</span> <span class="op">(</span><span class="fu"><a href="https://rdrr.io/r/base/interactive.html" class="external-link">interactive</a></span><span class="op">(</span><span class="op">)</span><span class="op">)</span> <span class="op">{</span></span></span>
<span class="r-in"><span></span></span>
<span class="r-in"><span><span class="va">ui</span> <span class="op">&lt;-</span> <span class="fu"><a href="fluidPage.html">fluidPage</a></span><span class="op">(</span></span></span>
<span class="r-in"><span> <span class="fu"><a href="selectInput.html">selectInput</a></span><span class="op">(</span><span class="st">"data"</span>, <span class="st">"Data Set"</span>, <span class="fu"><a href="https://rdrr.io/r/base/c.html" class="external-link">c</a></span><span class="op">(</span><span class="st">"mtcars"</span>, <span class="st">"pressure"</span><span class="op">)</span><span class="op">)</span>,</span></span>
<span class="r-in"><span> <span class="fu"><a href="checkboxGroupInput.html">checkboxGroupInput</a></span><span class="op">(</span><span class="st">"cols"</span>, <span class="st">"Columns (select 2)"</span>, <span class="fu"><a href="https://rdrr.io/r/base/character.html" class="external-link">character</a></span><span class="op">(</span><span class="fl">0</span><span class="op">)</span><span class="op">)</span>,</span></span>
<span class="r-in"><span> <span class="fu"><a href="plotOutput.html">plotOutput</a></span><span class="op">(</span><span class="st">"plot"</span><span class="op">)</span></span></span>
<span class="r-in"><span><span class="op">)</span></span></span>
<span class="r-in"><span></span></span>
<span class="r-in"><span><span class="va">server</span> <span class="op">&lt;-</span> <span class="kw">function</span><span class="op">(</span><span class="va">input</span>, <span class="va">output</span>, <span class="va">session</span><span class="op">)</span> <span class="op">{</span></span></span>
<span class="r-in"><span> <span class="fu"><a href="observe.html">observe</a></span><span class="op">(</span><span class="op">{</span></span></span>
<span class="r-in"><span> <span class="va">data</span> <span class="op">&lt;-</span> <span class="fu"><a href="https://rdrr.io/r/base/get.html" class="external-link">get</a></span><span class="op">(</span><span class="va">input</span><span class="op">$</span><span class="va">data</span><span class="op">)</span></span></span>
<span class="r-in"><span> <span class="co"># Sets a flag on input$cols to essentially do req(FALSE) if input$cols</span></span></span>
<span class="r-in"><span> <span class="co"># is accessed. Without this, an error will momentarily show whenever a</span></span></span>
<span class="r-in"><span> <span class="co"># new data set is selected.</span></span></span>
<span class="r-in"><span> <span class="fu">freezeReactiveValue</span><span class="op">(</span><span class="va">input</span>, <span class="st">"cols"</span><span class="op">)</span></span></span>
<span class="r-in"><span> <span class="fu"><a href="updateCheckboxGroupInput.html">updateCheckboxGroupInput</a></span><span class="op">(</span><span class="va">session</span>, <span class="st">"cols"</span>, choices <span class="op">=</span> <span class="fu"><a href="https://rdrr.io/r/base/names.html" class="external-link">names</a></span><span class="op">(</span><span class="va">data</span><span class="op">)</span><span class="op">)</span></span></span>
<span class="r-in"><span> <span class="op">}</span><span class="op">)</span></span></span>
<span class="r-in"><span></span></span>
<span class="r-in"><span> <span class="va">output</span><span class="op">$</span><span class="va">plot</span> <span class="op">&lt;-</span> <span class="fu"><a href="renderPlot.html">renderPlot</a></span><span class="op">(</span><span class="op">{</span></span></span>
<span class="r-in"><span> <span class="co"># When a new data set is selected, input$cols will have been invalidated</span></span></span>
<span class="r-in"><span> <span class="co"># above, and this will essentially do the same as req(FALSE), causing</span></span></span>
<span class="r-in"><span> <span class="co"># this observer to stop and raise a silent exception.</span></span></span>
<span class="r-in"><span> <span class="va">cols</span> <span class="op">&lt;-</span> <span class="va">input</span><span class="op">$</span><span class="va">cols</span></span></span>
<span class="r-in"><span> <span class="va">data</span> <span class="op">&lt;-</span> <span class="fu"><a href="https://rdrr.io/r/base/get.html" class="external-link">get</a></span><span class="op">(</span><span class="va">input</span><span class="op">$</span><span class="va">data</span><span class="op">)</span></span></span>
<span class="r-in"><span></span></span>
<span class="r-in"><span> <span class="kw">if</span> <span class="op">(</span><span class="fu"><a href="https://rdrr.io/r/base/length.html" class="external-link">length</a></span><span class="op">(</span><span class="va">cols</span><span class="op">)</span> <span class="op">==</span> <span class="fl">2</span><span class="op">)</span> <span class="op">{</span></span></span>
<span class="r-in"><span> <span class="fu"><a href="https://rdrr.io/r/graphics/plot.default.html" class="external-link">plot</a></span><span class="op">(</span><span class="va">data</span><span class="op">[[</span> <span class="va">cols</span><span class="op">[</span><span class="fl">1</span><span class="op">]</span> <span class="op">]</span><span class="op">]</span>, <span class="va">data</span><span class="op">[[</span> <span class="va">cols</span><span class="op">[</span><span class="fl">2</span><span class="op">]</span> <span class="op">]</span><span class="op">]</span><span class="op">)</span></span></span>
<span class="r-in"><span> <span class="op">}</span></span></span>
<span class="r-in"><span> <span class="op">}</span><span class="op">)</span></span></span>
<span class="r-in"><span><span class="op">}</span></span></span>
<span class="r-in"><span></span></span>
<span class="r-in"><span><span class="fu"><a href="shinyApp.html">shinyApp</a></span><span class="op">(</span><span class="va">ui</span>, <span class="va">server</span><span class="op">)</span></span></span>
<span class="r-in"><span><span class="op">}</span></span></span>
</code></pre></div>
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