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reactive expression is a expression whose result will change over time."><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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<span class="version label label-default" data-toggle="tooltip" data-placement="bottom" title="">1.8.0.9000</span>
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<h1>Create a reactive expression</h1>
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<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>
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<div class="hidden name"><code>reactive.Rd</code></div>
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</div>
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<div class="ref-description">
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<p>Wraps a normal expression to create a reactive expression. Conceptually, a
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reactive expression is a expression whose result will change over time.</p>
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</div>
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<div id="ref-usage">
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<div class="sourceCode"><pre class="sourceCode r"><code><span><span class="fu">reactive</span><span class="op">(</span></span>
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<span> <span class="va">x</span>,</span>
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<span> env <span class="op">=</span> <span class="fu"><a href="https://rdrr.io/r/base/sys.parent.html" class="external-link">parent.frame</a></span><span class="op">(</span><span class="op">)</span>,</span>
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<span> quoted <span class="op">=</span> <span class="cn">FALSE</span>,</span>
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<span> <span class="va">...</span>,</span>
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<span> label <span class="op">=</span> <span class="cn">NULL</span>,</span>
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<span> domain <span class="op">=</span> <span class="fu"><a href="domains.html">getDefaultReactiveDomain</a></span><span class="op">(</span><span class="op">)</span>,</span>
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<span> ..stacktraceon <span class="op">=</span> <span class="cn">TRUE</span></span>
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<span><span class="op">)</span></span>
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<span></span>
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<span><span class="fu">is.reactive</span><span class="op">(</span><span class="va">x</span><span class="op">)</span></span></code></pre></div>
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</div>
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<div id="arguments">
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<h2>Arguments</h2>
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<dl><dt>x</dt>
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<dd><p>For <code>is.reactive()</code>, an object to test. For <code>reactive()</code>, an expression. When passing in a <code><a href="https://rlang.r-lib.org/reference/defusing-advanced.html" class="external-link">quo()</a></code>sure with <code>reactive()</code>, remember to use <code><a href="https://rlang.r-lib.org/reference/inject.html" class="external-link">rlang::inject()</a></code> to distinguish that you are passing in the content of your quosure, not the expression of the quosure.</p></dd>
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<dt>env</dt>
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<dd><p>The parent environment for the reactive expression. By default,
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this is the calling environment, the same as when defining an ordinary
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non-reactive expression. If <code>x</code> is a quosure and <code>quoted</code> is <code>TRUE</code>,
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then <code>env</code> is ignored.</p></dd>
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<dt>quoted</dt>
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<dd><p>If it is <code>TRUE</code>, then the <code><a href="https://rdrr.io/r/base/substitute.html" class="external-link">quote()</a></code>ed value of <code>x</code>
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will be used when <code>x</code> is evaluated. If <code>x</code> is a quosure and you
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would like to use its expression as a value for <code>x</code>, then you must set
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<code>quoted</code> to <code>TRUE</code>.</p></dd>
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<dt>...</dt>
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<dd><p>Not used.</p></dd>
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<dt>label</dt>
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<dd><p>A label for the reactive expression, useful for debugging.</p></dd>
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<dt>domain</dt>
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<dd><p>See <a href="domains.html">domains</a>.</p></dd>
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<dt>..stacktraceon</dt>
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<dd><p>Advanced use only. For stack manipulation purposes; see
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<code><a href="stacktrace.html">stacktrace()</a></code>.</p></dd>
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</dl></div>
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<div id="value">
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<h2>Value</h2>
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<p>a function, wrapped in a S3 class "reactive"</p>
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</div>
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<div id="details">
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<h2>Details</h2>
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<p>Reactive expressions are expressions that can read reactive values and call
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other reactive expressions. Whenever a reactive value changes, any reactive
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expressions that depended on it are marked as "invalidated" and will
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automatically re-execute if necessary. If a reactive expression is marked as
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invalidated, any other reactive expressions that recently called it are also
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marked as invalidated. In this way, invalidations ripple through the
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expressions that depend on each other.</p>
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<p>See the <a href="https://shiny.rstudio.com/tutorial/" class="external-link">Shiny tutorial</a> for
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more information about reactive expressions.</p>
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</div>
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<div id="ref-examples">
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<h2>Examples</h2>
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<div class="sourceCode"><pre class="sourceCode r"><code><span class="r-in"><span><span class="kw"><a href="https://rdrr.io/r/base/library.html" class="external-link">library</a></span><span class="op">(</span><span class="va"><a href="https://rlang.r-lib.org" class="external-link">rlang</a></span><span class="op">)</span></span></span>
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<span class="r-in"><span><span class="va">values</span> <span class="op"><-</span> <span class="fu"><a href="reactiveValues.html">reactiveValues</a></span><span class="op">(</span>A<span class="op">=</span><span class="fl">1</span><span class="op">)</span></span></span>
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<span class="r-in"><span></span></span>
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<span class="r-in"><span><span class="va">reactiveB</span> <span class="op"><-</span> <span class="fu">reactive</span><span class="op">(</span><span class="op">{</span></span></span>
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<span class="r-in"><span> <span class="va">values</span><span class="op">$</span><span class="va">A</span> <span class="op">+</span> <span class="fl">1</span></span></span>
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<span class="r-in"><span><span class="op">}</span><span class="op">)</span></span></span>
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<span class="r-in"><span><span class="co"># View the values from the R console with isolate()</span></span></span>
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<span class="r-in"><span><span class="fu"><a href="isolate.html">isolate</a></span><span class="op">(</span><span class="fu">reactiveB</span><span class="op">(</span><span class="op">)</span><span class="op">)</span></span></span>
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<span class="r-out co"><span class="r-pr">#></span> [1] 2</span>
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<span class="r-in"><span><span class="co"># 2</span></span></span>
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<span class="r-in"><span></span></span>
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<span class="r-in"><span><span class="co"># To store expressions for later conversion to reactive, use quote()</span></span></span>
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<span class="r-in"><span><span class="va">myquo</span> <span class="op"><-</span> <span class="fu">rlang</span><span class="fu">::</span><span class="fu"><a href="https://rlang.r-lib.org/reference/defusing-advanced.html" class="external-link">quo</a></span><span class="op">(</span><span class="va">values</span><span class="op">$</span><span class="va">A</span> <span class="op">+</span> <span class="fl">2</span><span class="op">)</span></span></span>
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<span class="r-in"><span><span class="co"># Unexpected value! Sending a quosure directly will not work as expected.</span></span></span>
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<span class="r-in"><span><span class="va">reactiveC</span> <span class="op"><-</span> <span class="fu">reactive</span><span class="op">(</span><span class="va">myquo</span><span class="op">)</span></span></span>
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<span class="r-in"><span><span class="co"># We'd hope for `3`, but instead we get the quosure that was supplied.</span></span></span>
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<span class="r-in"><span><span class="fu"><a href="isolate.html">isolate</a></span><span class="op">(</span><span class="fu">reactiveC</span><span class="op">(</span><span class="op">)</span><span class="op">)</span></span></span>
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<span class="r-out co"><span class="r-pr">#></span> <span style="font-weight: bold;"><quosure></span></span>
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<span class="r-out co"><span class="r-pr">#></span> expr: <span style="color: #0000BB;">^values$A + 2</span></span>
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<span class="r-out co"><span class="r-pr">#></span> env: <span style="color: #0000BB;">0x560446837af8</span></span>
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<span class="r-in"><span></span></span>
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<span class="r-in"><span><span class="co"># Instead, the quosure should be `rlang::inject()`ed</span></span></span>
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<span class="r-in"><span><span class="va">reactiveD</span> <span class="op"><-</span> <span class="fu">rlang</span><span class="fu">::</span><span class="fu"><a href="https://rlang.r-lib.org/reference/inject.html" class="external-link">inject</a></span><span class="op">(</span><span class="fu">reactive</span><span class="op">(</span><span class="op">!</span><span class="op">!</span><span class="va">myquo</span><span class="op">)</span><span class="op">)</span></span></span>
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<span class="r-in"><span><span class="fu"><a href="isolate.html">isolate</a></span><span class="op">(</span><span class="fu">reactiveD</span><span class="op">(</span><span class="op">)</span><span class="op">)</span></span></span>
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<span class="r-out co"><span class="r-pr">#></span> [1] 3</span>
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<span class="r-in"><span><span class="co"># 3</span></span></span>
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<span class="r-in"><span></span></span>
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<span class="r-in"><span><span class="co"># (Legacy) Can use quoted expressions</span></span></span>
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<span class="r-in"><span><span class="va">expr</span> <span class="op"><-</span> <span class="fu"><a href="https://rdrr.io/r/base/substitute.html" class="external-link">quote</a></span><span class="op">(</span><span class="op">{</span> <span class="va">values</span><span class="op">$</span><span class="va">A</span> <span class="op">+</span> <span class="fl">3</span> <span class="op">}</span><span class="op">)</span></span></span>
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<span class="r-in"><span><span class="va">reactiveE</span> <span class="op"><-</span> <span class="fu">reactive</span><span class="op">(</span><span class="va">expr</span>, quoted <span class="op">=</span> <span class="cn">TRUE</span><span class="op">)</span></span></span>
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<span class="r-in"><span><span class="fu"><a href="isolate.html">isolate</a></span><span class="op">(</span><span class="fu">reactiveE</span><span class="op">(</span><span class="op">)</span><span class="op">)</span></span></span>
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<span class="r-out co"><span class="r-pr">#></span> [1] 4</span>
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<span class="r-in"><span><span class="co"># 4</span></span></span>
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<span class="r-in"><span></span></span>
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</code></pre></div>
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<p></p><p>Developed by Winston Chang, Joe Cheng, JJ Allaire, Carson Sievert, Barret Schloerke, Yihui Xie, Jeff Allen, Jonathan McPherson, Alan Dipert, Barbara Borges, Posit Software, PBC.</p>
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