r - how to delete warnings in reactive inputs in shiny -

could can tell me why error when change dataset in first selectinput widget? when change dataset diamonds mtcars error could not find 'carat' in input$bins , in plot 1 second , after works fine. why happened?

library(shiny) library(ggplot2)  data(diamonds) data(mtcars)   ui <- fluidpage(       column(3,              selectinput("data", "", choices = c('mtcars', 'diamonds')),              uioutput('server_cols'),              uioutput('server_bins')              ),       column(9,              plotoutput("plot")              )   )  server <- function(input, output) {        data <- reactive({             switch(input$data,                    diamonds = diamonds,                    mtcars = mtcars)       })        output$server_cols <- renderui({             data <- data()             nam <- colnames(data)             selectinput('cols', "choose numeric columns:", choices = nam[sapply(data, function(x) is.numeric(x))])       })        output$server_bins <- renderui({             if (!is.null(input$cols)) {                   df <- data()                   x <- eval(input$cols)                   max_value <- max(df[,x])                    sliderinput('bins','choose number of bins:', min = 0.1,                                max = max_value,                                value = max_value/2)              }       })        output$plot <- renderplot({             if (!is.null(input$cols) & !is.null(input$bins)) {                   basicdata <- data()                   var <- eval(input$cols)                    ggplot(basicdata, aes_string(var)) +                               geom_histogram(binwidth = input$bins, color = 'white', fill = 'red')             }            })  }  shinyapp(ui, server) 

your respective output objects respond changes of input variables. thus, when change dataset via input$data, plot rebuilds itself, although input$cols did not yet adjust. actually, try inserting print("a") inside output$plot see called 3 times if change input$data.

the fix rethink reaction logic , let elements respond specific changes, kind of response "thread".

for example, input$data should trigger output$server_cols. , output$server_bins should triggered input$cols (because implies input$data changed earlier). ultimately, output$plot has listen changes of input$bins (because changes in input$cols , input$data result in changes of input$bins since @ end of thread).

here suggestion using isolate.

library(shiny) library(ggplot2)  data(diamonds) data(mtcars)   ui <- fluidpage(   column(3,     selectinput("data", "", choices = c('mtcars', 'diamonds')),     uioutput('server_cols'),     uioutput('server_bins')    ),    column(9,      plotoutput("plot")    )     )  server <- function(input, output) {    data <- reactive({     switch(input$data, diamonds = diamonds, mtcars = mtcars)   })    output$server_cols <- renderui({     data <- data()     nam <- colnames(data)     selectinput('cols', "choose numeric columns:", choices = nam[sapply(data, function(x) is.numeric(x))])   })    output$server_bins <- renderui({     if (!is.null(input$cols)) {       df <- isolate(data())       x <- eval(input$cols)       max_value <- max(df[,x])        sliderinput('bins','choose number of bins:', min = 0.1, max = max_value, value = max_value/2)      }   })    output$plot <- renderplot({     if (!is.null(isolate(input$cols)) & !is.null(input$bins)) {       basicdata <- isolate(data())       var <- eval(isolate(input$cols))        ggplot(basicdata, aes_string(var)) +         geom_histogram(binwidth = input$bins, color = 'white', fill = 'red')     }       })     }  shinyapp(ui, server) 

you might want updateselectinput , updatesliderinput if want alter input elements depending on other input.