EVOLUTION-MANAGER

Edit File: freezeReactiveValue.html

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<table width="100%" summary="page for freezeReactiveVal {shiny}"><tr><td>freezeReactiveVal {shiny}</td><td style="text-align: right;">R Documentation</td></tr></table>

<h2>Freeze a reactive value</h2>

<h3>Description</h3>

<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
&quot;silent&quot; 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.
</p>

<h3>Usage</h3>

<pre>
freezeReactiveVal(x)

freezeReactiveValue(x, name)
</pre>

<h3>Arguments</h3>

<table summary="R argblock">
<tr valign="top"><td><code>x</code></td>
<td>
<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>
</td></tr>
<tr valign="top"><td><code>name</code></td>
<td>
<p>The name of a value in the <code><a href="reactiveValues.html">reactiveValues()</a></code> object.</p>
</td></tr>
</table>

<h3>Examples</h3>

<pre>
## Only run this examples in interactive R sessions
if (interactive()) {

ui &lt;- fluidPage(
  selectInput("data", "Data Set", c("mtcars", "pressure")),
  checkboxGroupInput("cols", "Columns (select 2)", character(0)),
  plotOutput("plot")
)

server &lt;- function(input, output, session) {
  observe({
    data &lt;- get(input$data)
    # Sets a flag on input$cols to essentially do req(FALSE) if input$cols
    # is accessed. Without this, an error will momentarily show whenever a
    # new data set is selected.
    freezeReactiveValue(input, "cols")
    updateCheckboxGroupInput(session, "cols", choices = names(data))
  })

output$plot &lt;- renderPlot({
    # When a new data set is selected, input$cols will have been invalidated
    # above, and this will essentially do the same as req(FALSE), causing
    # this observer to stop and raise a silent exception.
    cols &lt;- input$cols
    data &lt;- get(input$data)

if (length(cols) == 2) {
      plot(data[[ cols[1] ]], data[[ cols[2] ]])
    }
  })
}

shinyApp(ui, server)
}
</pre>

<hr /><div style="text-align: center;">[Package <em>shiny</em> version 1.5.0 <a href="00Index.html">Index</a>]</div>
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