Shiny observeEvent shows first event, but not second, third - r

TL;DR: observeEvent is only working on the first instance, but not subsequent.
Explanation:
In a small shiny app below, I dynamically build a URL based on user input, which points to the corresponding pre-rendered "timer" gif images I have hosted on GH. In this shiny app code below, observeEvent works great to pull the sliderInput value (e.g. 5sec), build a URL, and then clicking 'go' will show the timer using a clever shinyjs package. However, if I do not change the input (still 5sec), clicking go doesn't rebuild the image. If I change the value to a different number (4sec), it will show the correct gif. If I change back to the original number (5sec), no gif. If I go to a new number (3sec), correct gif. If I print the value of input$time or of rv$time in my observeEvent, then each of those values are updating correctly (both print the corresponding value).
Goal: to show the gif that corresponds to the input$time upon each update of input$go
Reprex:
library(shiny)
library(tidyverse)
library(glue)
library(shinyjs)
# Define UI
ui <- navbarPage(title = "Reprex",
## RHYME TIME -----
tabPanel("Time",
useShinyjs(),
sidebarLayout(
sidebarPanel(
sliderInput("time",
"Seconds",
min = 3,
max = 10,
value = 5
),
actionButton(inputId = "go",
label = "Go"),
),
mainPanel(
HTML("<center>"),
shinyjs::hidden(htmlOutput("simple_timer")),
HTML("</center>")
)
)
)
)
# Define server logic
server <- function(input, output, session) {
#a container to store my time var
rv <- reactiveValues(
time = 0
)
#the event that is triggered by input$go getting clicked
observeEvent(input$go, {
rv$time <- input$time #this should update rv$time after go is clicked
shinyjs::show("simple_timer") #this is the clever package with simple show/hide funs
})
#the reactive text that generates my HTML
output$simple_timer <- renderText({
glue::glue('<img src ="https://github.com/matthewhirschey/time_timer/raw/main/data/{rv$time}_sec.gif",
align = "center",
height="50%",
width="50%">')
})
}
# Run the application
shinyApp(ui = ui, server = server)

There are a couple of issues with your code:
renderText won't refire if you press input$go again (w/o changing the slider). Becasue the idea is that observer/render fires whenever their reactives change. As your renderText depends on rv$time which does not change when input$time does not change, the render function is not fired on subsequent button presses. This can be remedied by including input$go in the render function setting an additional dependency on the button.
This will not, however, solve your problem, because the browser uses caching. It sees that the <img> tag did not change (same src), thus it does not reload the picture. To circumvent that you can use the trick from Disable cache for some images by adding a timestamp to the src.
To make a long story short, this code does the trick:
output$simple_timer <- renderText({
input$go # make code dependent on the button
# add `?timestamp=<timestamp>`to the src URL to convince the browser to reload the pic
glue::glue('<img src ="https://github.com/matthewhirschey/time_timer/raw/main/data/{rv$time}_sec.gif?timestamp={Sys.time()}",
align = "center",
height="50%",
width="50%">')
})

Related

R Shiny : Refreshing plot when entering input OR pressing an action button

I'm fairly new to R Shiny but am stuck with the following problem for some time now and hope you can provide some help:
I try to refresh a plot in R shiny that should be refreshed if either a new input argument is entered OR an action button is pressed. This should be straightforward, but unfortunately I can't solve it, despite googling/reading instructions for some time. Any advice would be recommended. Any solutions on the web seem to put the whole renderplot function inside the observeEvent function, but I also need the renderplot in addition outside of it to account for the possibility of just entering inputs without pressing the action button.
I have no trouble creating a (render)plot that either exclusively is refreshed when entering a new input or exclusively refreshed when pressing a button.
However when doing both at the same I fail: I first tried to copy the renderplot function including the resulting output twice one time within an observeEvent function (to account for clicking the action button) and one time outside of an observeEvent (to account for only refreshing the inputs to the plot) but this leads only to a greyed out graph that refreshes after ~10 seconds delay when pressing the action button. I imagine adding the reactive click input generated from clicking the action button directly to the renderplot outside of observe event , but so far I couldn't get it to run. Any recommendations would be much appreciated.
Thank you in advance.
Like this?:
Edit: No need to pass the selectInput to the reactive Vals.. this does the same:
library(shiny)
ui <- fluidPage(
sidebarLayout(
sidebarPanel(
selectInput(inputId="select", label="title", choices=LETTERS[1:3], selected = "A"),
actionButton(inputId="btn", label="refresh")
),
mainPanel(
plotOutput("scatterPlot")
)
)
)
server <- function(input, output) {
plotSettings <- reactiveValues()
observeEvent(c(input$btn, input$select), {
plotSettings$values <- runif(100,1,100)
# plotSettings$title <- input$select
}, ignoreNULL = FALSE)
output$scatterPlot <- renderPlot({
plot(plotSettings$values, main=input$select)
})
}
shinyApp(ui = ui, server = server)

Optimizing Shiny Performance with Tabs and suspendWhenHidden = FALSE

I've got a Flexdashboard-based Shiny application with several tabs, and within each tab, grids of multiple plots. Performance is a bit of an issue, particularly when deployed on the free Shiny Server.
Initially, the main issue was that clicking each tab would require re-rendering of the plots. I set the suspendWhenHidden option to be FALSE, and this helps - Now switching the input has a slow delay to load all the plots, but at least when navigating the UI, performance is snappy.
This got me thinking, however - is there any way to achieve a hybrid of the two behaviors? So say I'm on an active tab which just produces a single plot. This plot renders quickly. Can we tell shiny to render this plot, display it to the user, and then in the background, continue loading all the elements of the other tabs? As it stands now, the active tab will not finish rendering the plot until all plots on the hidden tabs are also rendered.
In summary, a hybrid suspendWhenHidden = FALSE and TRUE:
Render the active tab elements first, display to the user, then
Continue rendering the elements on the hidden tabs
I thought perhaps setting priority might achieve this, but it doesn't seem to work. Any thoughts or suggestions?
Here's a minimal reproducible example. The goal would be for the first plot (in tab 1) to render and appear before beginning rendering of the second plot (in tab 2) - But the plot should start rendering in tab 2 without requiring a click of tab 2.
library(shiny)
ui <- fluidPage(
sidebarLayout(
sidebarPanel(
numericInput('n', 'Size', 10)
),
mainPanel(
tabsetPanel(
tabPanel("Tab1", plotOutput("plot1")),
tabPanel("Tab2", plotOutput("plot2"))))
)
)
# Define the server code
server <- shinyServer(function(input, output, session) {
output$plot1 <- renderPlot({plot(1:input$n)},height = 400,width=800)
output$plot2 <- renderPlot({ Sys.sleep(5); plot(1:input$n,col="red")},height = 400,width=800)
outputOptions(output, "plot2", suspendWhenHidden = FALSE)
})
# Return a Shiny app object
shinyApp(ui = ui, server = server)
There is two ways to achieve this
Load all the tabs and then show the output
Use eventReactive to activate the other tabs
For the first option just put below additionally
outputOptions(output, "plot1", suspendWhenHidden = FALSE)
and if you want reactivity write eventReactive functions for each tab.

R Shiny: Is there a way to check if a button is disabled using shinyjs package?

Is there a way to check if a download button is disabled using the shinyjs R package? I want to use shinyjs or something similar because they have very easy syntax. This is my package:
server.R:
library(shiny)
library(shinyjs)
library(shinyBS)
shinyServer(function(input, output) {
observe({
shinyjs::disable("download1")
if(shinyjs::is.disabled("download1")){ ## This is what I am trying to do
# Do something
}
})
})
ui.R
shinyUI(fluidPage(
downloadButton("download1")
))
Not directly (well, not easily*).
Buttons can only be disabled when you decide to disable them, so you can have some sort of a reactive variable that holds whether or not the button should be disabled, and whenever you disable the button, you also change the value of that variable. In order to make sure they stay in sync, every time you want to disable the button you can set the variable to mirror that, and then you can use shinyjs::toggleState(condition = variable) so that the disabled state will mirror what the variable says.
Example code to illustrate what I mean:
library(shiny)
ui <- fluidPage(
shinyjs::useShinyjs(),
numericInput("num", "When divisible by 3, disable the button", 1),
actionButton("btn", "button")
)
server <- function(input, output, session) {
values <- reactiveValues(disable = FALSE)
observe({
values$disable <- (input$num %% 3 == 0)
})
observe({
shinyjs::toggleState("btn", condition = !values$disable)
})
}
shinyApp(ui = ui, server = server)
In this app, whenever you want to disable the button, simply set values$disable to FALSE and to enable the button set it to TRUE. To check if the button is currently on or off at any point in time, you can look at the value of values$disable.
*I'm guessing that you wanted a more direct approach to ask the app a question in real time "hey shiny, is button X currently disabled?". You can do that, but it would involve writing custom javascript code to check for the button state, and for custom code to ask javascript that question and to listen for its response. This would work and be guaranteed to be correct, but it's likely overkill for most cases.

Can I save the old value of a reactive object when it changes?

Note: After coming up with the answer I reworded the question to make if clearer.
Sometimes in a shiny app. I want to make use of a value selected by the user for a widget, as well as the previous value selected for that same widget. This could apply to reactive values derived from user input, where I want the old and the new value.
The problem is that if I try to save the value of a widget, then the variable containing that value has to be reactive or it will not update every time the widget changes. But, if I save the the value in a reactive context it will always give me the current value, not the previous one.
How can I save the previous value of a widget, but still have it update every time the user changes the widget?
Is there a way that does not require the use of an actionButton every time the user changes things? Avoiding an actionButton can be desirable with adding one is otherwise unnecessary and creates excess clicking for the user.
Seeing as the session flush event method seems to be broken for this purpose, here is an alternative way to do it using an observeEvent construct and a reactive variable.
library(shiny)
ui <- fluidPage(
h1("Memory"),
sidebarLayout(
sidebarPanel(
numericInput("val", "Next Value", 10)
),
mainPanel(
verbatimTextOutput("curval"),
verbatimTextOutput("lstval")
)
)
)
server <- function(input,output,session) {
rv <- reactiveValues(lstval=0,curval=0)
observeEvent(input$val, {rv$lstval <- rv$curval; rv$curval <- input$val})
curre <- reactive({req(input$val); input$val; rv$curval})
lstre <- reactive({req(input$val); input$val; rv$lstval})
output$curval <- renderPrint({sprintf("cur:%d",curre())})
output$lstval <- renderPrint({sprintf("lst:%d",lstre())})
}
options(shiny.reactlog = TRUE)
shinyApp(ui, server)
Yielding:
Update This answer was posted before the advent of the reactiveValues/observeEvent model in shiny. I think that #MikeWise 's answer is the better way to do this.
After some playing around this is what I came up with. The ui.r is nothing special
ui.r
library(shiny)
ui <- shinyUI(fluidPage(
sidebarLayout(
sidebarPanel(
selectizeInput(inputId="XX", label="Choose a letter",choices=letters[1:5])
),
mainPanel(
textOutput("Current"),
textOutput("old")
)
)
))
"Current" will display the current selection and "old" displays the previous selection.
In the server.r I made use of three key functions: reactiveValues, isolate and session$onFlush.
server.r
library(shiny)
server <- function(input, output,session) {
Values<-reactiveValues(old="Start")
session$onFlush(once=FALSE, function(){
isolate({ Values$old<-input$XX })
})
output$Current <- renderText({paste("Current:",input$XX)})
output$old <- renderText({ paste("Old:",Values$old) })
}
The server.r works like this.
First, Values$old is created using the reactiveValues function. I gave it the value "Start" to make it clear what was happening on load up.
Then I added a session$onFlush function. Note that I have session as an argument in my server function. This will run every time that shiny flushes the reactive system - such as when the selectizeInput is changed by the user. What is important is that it will run before input$XX gets a new value - so the value has changed at the selectizeInput but not at XX.
Inside the session$onFlush I then assign the outgoing value of XX to Values$old. This is done inside an isolate() as this will prevent any problems with input$XX gets updated with the new values. I can then use input$XX and Values$old in the renderText() functions.

Shiny - Taking Text input into auxiliary function

I am new to Shiny and trying to build a more accessible input and output for a function I built. I am giving this to people that don't run R so trying to build something that runs my functions in the background and then spits out the answer.
I am having some trouble getting everything in the way that I want it unfortunately and dealing with a bunch of errors. However, here is my more pointed question:
The actual function that I want to run takes a name (in quotations as "Last,First") and a number.
PredH("Last,First",650)
So I want a shiny application that takes a name input and a number input that then runs this program and then spits back out a data table with my answer. So a couple of questions.
How do I get it in the right form to input into my equation on the server side script, do I need to return it in the function so it can be accessed using a function$table type access? (Right now I am just printing using cat() function in the console for the function but know that may not be usable for this type of application.
I want to return a dataframe that can be gotten at PredH14$table. How do I go about building that shiny?
Here is my code so far:
UI:
library(shiny)
shinyUI(pageWithSidebar(
# Application title
headerPanel("Miles Per Gallon"),
# Sidebar with controls to select the variable to plot against mpg
# and to specify whether outliers should be included
sidebarPanel(
textInput("playername", "Player Name (Last,First):", "Patch,Trevor"),
radioButtons("type", "Type:",
list("Pitcher" = "P",
"Hitter" = "H"
)),
numericInput("PAIP", "PA/IP:", 550),
submitButton("Run Comparables")
),
mainPanel(
textOutput("name")
)
Server:
library(shiny)
shinyServer(function(input, output) {
sliderValues <- reactive({
data.frame(
Name = c("name", "PA"),
Value = c(as.character(playername),
PAIP),
stringsAsFactors=FALSE)
})
name=input[1,2]
PAIP=input[2,2]
testing <- function(name,PAIP){
a=paste(name,PAIP)
return(a) }
output$name=renderText(testing$a)
})
I am not quite sure I understood your question 100% but I clearly see you are wondering how to pass the input of the UI into the server and maybe, the other way back.
In your server code, clearly you are not getting any input from the UI. Basically you have created three input variables in your ui.R:
1. input$playername
2. input$type
3. input$PAIP
And one output:
1. output$name
Just let you know, the function sliderValues <- reactive(..) is called every time there is any input from the input... like people click the dropdown list or people modifies words in the text box.
You can even get started without the submit button just to get started. But the existence of the submit button actually makes everything easier. Create a submit button for an input form. Forms that include a submit button do not automatically update their outputs when inputs change, rather they wait until the user explicitly clicks the submit button.
So you can put your code in a way similar like this:
# server.R
library(shiny)
shinyServer(function(input, output) {
sliderValues <- reactive({
result <- ... input$playername ... input$type ... input$PAIP
return(result)
})
output$name <- renderPlot/renderText (... sliderValues...)
})
# ui.R
library(shiny)
shinyUI(pageWithSidebar(
headerPanel("Miles Per Gallon"),
sidebarPanel(
textInput("playername" ... ),
radioButtons("type" ... ),
numericInput("PAIP" ... ),
submitButton("...")
),
mainPanel(
textOutput/plotOutput...("name")
)
))
In the end, check out the shiny example that might be what you want.
library(shiny)
runExample('07_widgets')

Resources