R Shiny: actionButton to generate random value from input values and render plot

I have made a simple shiny app that generates a plot of the x and y data from an individual group within the data which the users can choose from. The app subsets the larger dataframe and produces the graph for only the chosen individual. I would also like to include and actionButton which chooses an individual from within the dataset at random and plots that every time the button is pushed.

library(shiny)
library(tidyverse)
# Create example data frame
Data <- data.frame(Indiv = c(rep(1,10),
rep(2,10),
rep(3,10),
rep(4,10),
rep(5,10),
rep(6,10)),
varX = c(runif(10, min = 1, max = 10),
runif(10, min = 1, max = 10),
runif(10, min = 1, max = 10),
runif(10, min = 1, max = 10),
runif(10, min = 1, max = 10),
runif(10, min = 1, max = 10)),
varY = c(runif(10, min = 1, max = 1),
runif(10, min = 1, max = 5),
runif(10, min = 1, max = 10),
runif(10, min = 1, max = 15),
runif(10, min = 1, max = 20),
runif(10, min = 1, max = 25))
)
######   Shiny App   #######
# User interface for shiny app
ui <- fluidPage(
titlePanel("Random Select Button"), # page title
sidebarLayout(
# Sidebar panel 
sidebarPanel(
# input for which TagID to display in plot
actionButton("do", "Plot Random Indiv"),
selectInput(inputId = "ID",
label = "Individual ID",
choices = levels(factor(Data$Indiv)), 
selected = NULL, # choose no individuals by default
multiple = FALSE     # allow for multiple options
),
p("Choose an invidual, or push the button to randomly choose an individual."),
),
# Main Panel
mainPanel(
plotOutput("IndivPlot"), # name of plot object
),
)
)
# Server
server <- function(input, output) {
# Plot
output$IndivPlot <- renderPlot({ # make a live adjustable plot
### Filter to only include selected Individual
Data <- Data[Data$Indiv %in% input$ID,] 
# Create plot
p = ggplot(data=Data, aes(x=varX, y=varY))+
geom_line()+
expand_limits(y=c(1,30), x = c(1,10))+
scale_y_continuous(breaks=seq(1,30,5), labels=seq(1,30,5))+
scale_x_continuous(breaks = seq(1,10,1), labels = seq(1,10,1))+ 
labs(x = "My X", y = "My Y")  
print(p)
})
}
shinyApp(ui = ui, server = server)

I can't figure out how to get the action button to randomly choose and individual ID number and cause the plot to render. Right now, the button exists on the UI but doesn't do anything.

You may create a reactive ID which will be dynamic. It will be updated when the ID is selected from the dropdown as well as when the action button is pressed to generate random ID.

The plot will be updated based on the ID.

library(shiny)
library(tidyverse)
######   Shiny App   #######
# User interface for shiny app
ui <- fluidPage(
titlePanel("Random Select Button"), # page title
sidebarLayout(
# Sidebar panel 
sidebarPanel(
# input for which TagID to display in plot
actionButton("do", "Plot Random Indiv"),
selectInput(inputId = "ID",
label = "Individual ID",
choices = levels(factor(Data$Indiv)), 
selected = NULL, # choose no individuals by default
multiple = FALSE     # allow for multiple options
),
p("Choose an invidual, or push the button to randomly choose an individual."),
),
# Main Panel
mainPanel(
plotOutput("IndivPlot"), # name of plot object
),
)
)
# Server
server <- function(input, output, session) {
#To save dynamic ID
rv <- reactiveValues()
observe({
#ID selected from the dropdown manually
rv$ID <- input$ID
})
# Plot
output$IndivPlot <- renderPlot({ # make a live adjustable plot
### Filter to only include selected Individual
Data <- Data[Data$Indiv %in% rv$ID,] 
# Create plot
p = ggplot(data=Data, aes(x=varX, y=varY))+
geom_line()+
expand_limits(y=c(1,30), x = c(1,10))+
scale_y_continuous(breaks=seq(1,30,5), labels=seq(1,30,5))+
scale_x_continuous(breaks = seq(1,10,1), labels = seq(1,10,1))+ 
labs(x = "My X", y = "My Y")  
print(p)
})
#On action button click
observeEvent(input$do, {
#Select a random ID
rv$ID <- sample(unique(Data$Indiv), 1)
#Update the value of dropdown with random ID selected
updateSelectInput(session, inputId = "ID",
label = "Individual ID",
choices = levels(factor(Data$Indiv)), 
selected = rv$ID)
})
}
shinyApp(ui = ui, server = server)