How do I reference the values in a reactive variable - r

Question

I am trying to reference the values of a reactive variable. I have included the code I have so far below. I am referring to "output$var1" below. This app selects the dataset and based on that dataset produces another selectInput to select a variable.
I am able to render the text if I directly type dataset$area (the first variable of the rock dataset). I would like to render something like "dataset$selvar". Is there a way to do this?
library(shiny)
# Define UI for application that draws a histogram
ui <- fluidPage(
sidebarLayout(
sidebarPanel(
selectInput("dataset", label = "Dataset", choices =c("rock","pressure","cars")),
numericInput(inputId = "obs",
label = "Number of observations to view:",
value=10)
),
mainPanel(
verbatimTextOutput("summary"),
tableOutput("table"),
selectInput("inSelect","Select variable", c("Item A", "Item B")),
textOutput("var1")
)
)
)
# Define server logic required to draw a histogram
server <- function(input, output, session) {
datasetInput<-reactive({
switch(input$dataset,
"rock"=rock,
"pressure"=pressure,
"cars"=cars
)
})
output$summary<- renderPrint({
dataset<- datasetInput()
summary(dataset)
})
output$table<- renderTable({
head(datasetInput(), n=input$obs)
})
observe({
dataset<- datasetInput()
varlist<-colnames(dataset)
updateSelectInput(session,"inSelect",
label="Select variable",
choices=varlist,
selected=head(varlist,1)
)
selvar<-updateSelectInput(session,"inSelect",
label="Select variable",
choices=varlist,
selected=head(varlist,1)
)
output$var1<-renderText({
dataset$area
})
})
}
# Run the application
shinyApp(ui = ui, server = server)
When I try dataset$selvar I get "error i ncat: argument 1 (type 'environment') cannot be bandled by 'cat'

Answer 1

Remove the second updateSelectInput from your observer, move your renderText outside of the observer. and inside the renderText use datasetInput()[[input$inSelect]] to display the select column from the selected dataset.
library(shiny)
ui <- fluidPage(
sidebarLayout(
sidebarPanel(
selectInput("dataset", label = "Dataset", choices = c("rock", "pressure", "cars")),
numericInput(
inputId = "obs",
label = "Number of observations to view:",
value = 10
)
),
mainPanel(
verbatimTextOutput("summary"),
tableOutput("table"),
selectInput("inSelect", "Select variable", c("Item A", "Item B")),
textOutput("var1")
)
)
)
server <- function(input, output, session) {
datasetInput <- reactive({
switch(input$dataset,
"rock" = rock,
"pressure" = pressure,
"cars" = cars
)
})
output$summary <- renderPrint({
dataset <- datasetInput()
summary(dataset)
})
output$table <- renderTable({
head(datasetInput(), n = input$obs)
})
observe({
dataset <- datasetInput()
varlist <- colnames(dataset)
updateSelectInput(session, "inSelect",
label = "Select variable",
choices = varlist,
selected = varlist[[1]]
)
})
output$var1 <- renderText({
datasetInput()[[input$inSelect]]
})
}
# Run the application
shinyApp(ui = ui, server = server)
#>
#> Listening on http://127.0.0.1:5275