Code for a reactive table to plot in Shiny - r

Question

I'm new to shiny, and I am trying to do a simple density plot where there are 2 groups of data, with reactive 'shifts' in the mean etc.
A simplified summary of this is that one set of data has a mean of 0, and variance of 1. The second set of data has a mean of shift, which is defined in a slider.
I have tried to use reactiveValues, as shown in the code below to store the matrix of observations d1, generated from the density function y values, and the corresponding x values are stored in x.
library(shiny)
# Define UI for application that draws a histogram
ui <- fluidPage(
# Application title
titlePanel("Old Faithful Geyser Data"),
# Sidebar with a slider input for number of bins
sidebarLayout(
sidebarPanel(
sliderInput("shift",
"shift of 2nd set",
min = -1,
max = 1,
value = 0)
),
# Show a plot of the generated distribution
mainPanel(
plotOutput("distPlot")
)
)
)
# Define server logic required to draw a histogram
server <- function(input, output) {
data <- reactiveValues({
d1 <- matrix(nrow=100, ncol=512)
for(i in 1:70){
d1[i,] <- density(rnorm(1000),from = -3, to = 3)$y
}
for(i in 71:100){
d1[i,] <- density(rnorm(1000, input$shift),from = -3, to = 3)$y
}
x <- density(rnorm(1000),from = -3, to = 3)$x
})
output$distPlot <- renderPlot({
matplot(data$x, t(data$d1), type = "l", lty = 1, col = c(rep(1,70),rep(2,30)))
})
}
# Run the application
shinyApp(ui = ui, server = server)
The above code is largely from the example shiny app, so please excuse any generic references. It should still work.
I was expecting a shiny plot with a slider on the left, and a plot on the right with 100 density lines in 2 colours. When the shift slider is changed the second set of data (red) will slide left or right depending on the shift.
Instead, I get the error message
55: stop
54: .getReactiveEnvironment()$currentContext
53: .subset2(x, "impl")$get
52: $.reactivevalues
47: server [/beavis/Documents/test/app.R#37]
Error in .getReactiveEnvironment()$currentContext() :
Operation not allowed without an active reactive context. (You tried to do something that can only be done from inside a reactive expression or observer.)
Is anyone able to help me fix this code? Any help will be greatly appreciated. Having played around for an hour I believe the issue lies in the reactiveValues section, but nothing so far has worked.

Answer 1

Nice try. You're quite close. What you're missing is two things. You are creating a data object, which becomes reactive (I use reactive instead). This means that whenever you are calling data, you need to call it as data().
Second, your data returns only x. Output of this reactive environment should in your case be a list of x and d1.
library(shiny)
# Define UI for application that draws a histogram
ui <- fluidPage(
# Application title
titlePanel("Old Faithful Geyser Data"),
# Sidebar with a slider input for number of bins
sidebarLayout(
sidebarPanel(
sliderInput("shift",
"shift of 2nd set",
min = -1,
max = 1,
value = 0,
step = 0.1) # I added a step
),
# Show a plot of the generated distribution
mainPanel(
plotOutput("distPlot")
)
)
)
# Define server logic required to draw a histogram
server <- function(input, output) {
# This reactive environment can be accessed using data().
data <- reactive({
d1 <- matrix(nrow=100, ncol=512)
for(i in 1:70){
d1[i,] <- density(rnorm(1000),from = -3, to = 3)$y
}
for(i in 71:100){
d1[i,] <- density(rnorm(1000, input$shift),from = -3, to = 3)$y
}
x <- density(rnorm(1000), from = -3, to = 3)$x
list(x = x, d1 = d1) # make sure that all objects are returned
})
output$distPlot <- renderPlot({
matplot(data()$x, t(data()$d1), type = "l", lty = 1, col = c(rep(1,70),rep(2,30)))
})
}
# Run the application
shinyApp(ui = ui, server = server)