Shiny - Input Argument Not Accessible - r

Question

I'm trying to take input from a slider in shiny and use it in the server section by calling a function on it to obtain information for graphing. However, the input from the slider is not recognized serverside, and throws an error.
Evaluation error: argument "hour" is missing, with no default.
The inputID matches the argument so I don't understand why it wouldn't be able to access it.
library(shiny)
library(shinydashboard)
get_data <- function(foo){return(foo)}
#build shiny app
header <- dashboardHeader(
title="Data"
)
sidebar <- dashboardSidebar(
sidebarMenu(
menuItem("Charts and Analysis", tabName = "charts", icon = icon("bar-chart-o"),
menuSubItem("Temperature by Time of Day", tabName = "temperatures", icon = NULL) )
)
)
body <- dashboardBody(
tabItems(
tabItem(tabName = "temperatures",
fluidRow(
box(
title = "Time of Day",
sliderInput(inputId = "hour", label="Hour (military)", min=0, max=23, value=12, step=1)
),
box(plotOutput("series"))
)
)
)
)
ui <- dashboardPage(skin="green", header, sidebar, body)
server <- function(input, output) {
MR <- get_data(strtoi(input$hour))
output$series <- renderPlot({
plot(x=MR, y=MR)
})
}
shinyApp(ui, server)

Answer 1

In a shiny application calls to input parameters must be in a reactive context.
Then we must move the functional assignment into the renderPlot function.
library(shiny)
library(shinydashboard)
get_data <- function(foo){return(foo)}
#build shiny app
header <- dashboardHeader(
title="Data"
)
sidebar <- dashboardSidebar(
sidebarMenu(
menuItem("Charts and Analysis", tabName = "charts", icon = icon("bar-chart-o"),
menuSubItem("Temperature by Time of Day", tabName = "temperatures", icon = NULL) )
)
)
body <- dashboardBody(
tabItems(
tabItem(tabName = "temperatures",
fluidRow(
box(
title = "Time of Day",
sliderInput(inputId = "hour", label="Hour (military)", min=0, max=23, value=12, step=1)
),
box(plotOutput("series"))
)
)
)
)
ui <- dashboardPage(skin="green", header, sidebar, body)
server <- function(input, output) {
output$series <- renderPlot({
MR <- get_data(strtoi(input$hour))
plot(x=MR, y=MR)
})
}
shinyApp(ui, server)