Having problems with using reactive inputs in shiny

Question

I am new to using Shiny with R. I have to develop a web app to display graphs based on the range of years. Shiny server has to take inputs from ui (starting year and ending year) and make calculations and plot the outputs. I have written R script to make a vector named years with the different years in the range selected and bind it to a data frame. Then, its followed by adding new calculated columns to the table and plotting different columns. This is the code

library(shiny)
ui <- fluidPage(
  sliderInput(inputId = "startyear", 
              label = "Choose starting year", 
              value = 25, min = 2016, max = 2050),
  sliderInput(inputId = "endyear", 
              label = "Choose ending year", 
              value = 25, min = 2016, max = 2050),
  plotOutput("plot1"),
  plotOutput("plot2"),
  plotOutput("plot3")

  )

server <- function(input, output) {
  years <- reactive({(input$startyear:input$endyear)})
  sample <- data.frame(years)
  sample$timestepdays <- (sample$years-min(sample$years))*365
  sample$timestep <- (sample$years-min(sample$years))
  sample$pop <- sample$timestepdays *500 +839000
  sample$no_of_trips <- sample$pop*4.4045
  sample$NE <- sample$no_of_trips*0.00000003+0.3738
  sample$Delta_VE_logit <- sample$timestep*(-0.149) +5 
  sample$Delta_VE <- (exp(sample$Delta_VE_logit)/(exp(sample$Delta_VE_logit)+1))*(1-0.5)+0.5
  sample$VMT <- 7.3 * sample$no_of_trips
  sample$ER_per_mile <- sample$Delta_VE * sample$NE
  sample$CO2 <- (sample$ER_per_mile * sample$VMT ) /10000

 output$plot1 <- renderPlot({lines.default(sample&years,sample$population)})
   output$plot2 <- renderPlot({lines.default(sample&years,sample$no_of_trips)})
     output$plot3 <- renderPlot({lines.default(sample&no_of_trips,sample$NE)})

}

shinyApp(ui = ui, server = server)

I am getting the following errors

Warning: Error in as.data.frame.default: cannot coerce class "c("reactiveExpr", "reactive")" to a data.frame
Stack trace (innermost first):
    40: as.data.frame.default
    39: as.data.frame
    38: data.frame
    37: server [C:/Users/R-Jaikumar/Downloads/shiny-quickstart-1/downloads/code/01-template.R#17]
     1: runApp
Error in as.data.frame.default(x[[i]], optional = TRUE) : 
  cannot coerce class "c("reactiveExpr", "reactive")" to a data.frame

Once you make a variable reactive({}), you need to refer to it as variable() from then on. So sample <- data.frame(years) should be sample <- data.frame(years()). — Balter
Hey, Thanks, I am getting the following error after amending the changes. 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. — rohit j
I guess that is about sample, that should be a reactive but not a data.frame — Sean Lin

Sean Lin Sean Lin · Accepted Answer · 2017-08-09T19:48:56

I think make sample as a reactive object shall work, and a function name is not a good choice as a name of a data frame. Not quite sure what you are plotting, but you may change it later. Try code below:

library(shiny)
ui <- fluidPage(
    sliderInput(inputId = "startyear", 
            label = "Choose starting year", 
            value = 25, min = 2016, max = 2050),
    sliderInput(inputId = "endyear", 
            label = "Choose ending year", 
            value = 25, min = 2016, max = 2050),
    plotOutput("plot1"),
    plotOutput("plot2"),
    plotOutput("plot3")
)

server <- function(input, output) {
years <- reactive({(input$startyear:input$endyear)})
sam <- reactive({
    years = years()
    timestepdays <- (years-min(years))*365
    timestep <- (years-min(years))
    pop <- timestepdays *500 +839000
    no_of_trips <- pop*4.4045
    NE <- no_of_trips*0.00000003+0.3738
    Delta_VE_logit <- timestep*(-0.149) +5
    Delta_VE <- (exp(Delta_VE_logit)/(exp(Delta_VE_logit)+1))*(1-0.5)+0.5
    VMT <- 7.3 * no_of_trips
    ER_per_mile <- Delta_VE * NE
    CO2 <- (ER_per_mile * VMT ) /10000
    sam = data.frame(years, timestepdays, timestep, pop, no_of_trips, NE, Delta_VE_logit, 
                     Delta_VE, VMT, ER_per_mile, CO2)
    })


output$plot1 <- renderPlot({
    line(sam()$years,sam()$pop)
})
output$plot2 <- renderPlot({
    line(sam()$years,sam()$no_of_trips)
})
output$plot3 <- renderPlot({
    line(sam()$no_of_trips,sam()$NE)
})
}

shinyApp(ui = ui, server = server)

Having problems with using reactive inputs in shiny

1 Answers