How to calculate an mathematic expresion reciving values from sliders - r

Question

I am new in Shiny and i am trying to learn. My issue is that i want to calculate an mathematic expresion by giving a value from slider and in the end to show the result. Until now i have made the following code but it is wrong. Could you please guide me.
Thanks in advance
library(shiny)
library(shinythemes)
# Define UI for slider demo app ----
ui <- fluidPage(
#Navbar structure for UI
navbarPage("SAR Model", theme = shinytheme("united"),
tabPanel("Toblers Function", fluid = TRUE),
# App title ----
titlePanel("Toblers Fuction"),
# Sidebar layout with input and output definitions ----
sidebarLayout(
# Sidebar to demonstrate various slider options ----
sidebarPanel(
# Input: Slope interval with step value ----
sliderInput("slope", "Slope:",
min = -0.60, max = 0.50,
value = 0.0, step = 0.01),
),
# Main panel for displaying outputs ----
mainPanel(
# Output: Table summarizing the values entered ----
tableOutput("values")
)
)
)
)
server <- function(input, output, session) {
# Reactive expression to create data frame off input value ----
sliderValues <- reactive({
data.frame(
Name = c("Slope"),
Value = as.character(c(input$slope)),
stringsAsFactors = FALSE)
})
Value$toblers <- 6*exp(-3.5*input$slope)
# Show the values in an HTML table ----
output$values <- renderTable({
sliderValues()
})
output$tobler <-renderText({value$toblers})
}
shinyApp(ui = ui, server = server)

Answer 1

You use input$slope outside of a reactive context which is not allowed. Define a reactive for your calculation of toblers and then display this, like:
toblers <- reactive({
6*exp(-3.5*input$slope)
})
output$tobler <-renderText({toblers()})

Answer 2

Ok i made some changes but does not show the result.
Here is the code
library(shiny)
library(shinythemes)
# Define UI for slider demo app ----
ui <- fluidPage(
#Navbar structure for UI
navbarPage("SAR Model", theme = shinytheme("united"),
tabPanel("Toblers Function", fluid = TRUE),
# App title ----
titlePanel("Toblers Fuction"),
# Sidebar layout with input and output definitions ----
sidebarLayout(
# Sidebar to demonstrate various slider options ----
sidebarPanel(
# Input: Slope interval with step value ----
sliderInput("slope", "Slope:",
min = -0.60, max = 0.50,
value = 0.0, step = 0.01)),
# Main panel for displaying outputs ----
mainPanel(
# Output: Table summarizing the values entered ----
tableOutput("values"),
)
)
)
)
server <- function(input, output, session) {
# Reactive expression to create data frame off input value ----
sliderValues <- reactive({
data.frame(
Name = c("Slope"),
Value = as.character(c(input$slope)),
stringsAsFactors = TRUE)
})
# Show the values in an HTML table ----
output$values <- renderTable({
sliderValues()
})
output$slope <- renderText({
paste0("The speed is ", 6*exp(-3.5*input$slope),"Km/h")
})
}
shinyApp(ui = ui, server = server)

Answer 3

I found a solution but know does not appear the table with the value from slider.
Any opinion why?
here is the code
library(shiny)
library(shinythemes)
# Define UI for slider demo app ----
ui <- fluidPage(
#Navbar structure for UI
navbarPage("SAR Model", theme = shinytheme("united"),
tabPanel("Toblers Function", fluid = TRUE),
# App title ----
titlePanel("Toblers Fuction"),
# Sidebar layout with input and output definitions ----
sidebarLayout(
# Sidebar to demonstrate various slider options ----
sidebarPanel(
# Input: Slope interval with step value ----
sliderInput("slope", "Slope:",
min = -0.60, max = 0.50,
value = 0.0, step = 0.01)),
# Main panel for displaying outputs ----
mainPanel(
# Output: Table summarizing the values entered ----
tableOutput("Values"),
tableOutput("slope")
)
)
)
)
server <- function(input, output, session) {
# Reactive expression to create data frame off input value ----
sliderValues <- reactive({
data.frame(
Name = c("Slope"),
Value = as.character(c(input$slope)),
stringsAsFactors = TRUE)
})
# Show the values in an HTML table ----
output$values <- renderTable({
sliderValues()
})
output$slope <- renderText({
paste0("The speed is ", 6*exp(-3.5*abs(input$slope+0.05)),"Km/h")
})
}
shinyApp(ui = ui, server = server)