R shiny render UI does not work

Question

In my application, I ask the user to input a file (.csv). Further there are two selectInput(s) which are populated with column names from the input file using renderUI(). As user selects two different columns and click submitButton a plot is generated. The UI with ideal output is given below. This works because i have manually input the values in plot and it does not take the columns as selected in drop down options.

correct output

I think the problem is converting factor type elements in dataframe to numeric type which can be plotted.

the error image :

server.R

library(shiny)
shinyServer(function(input, output) {

 lastgang <- reactive({
  if(is.null(input$file)){return()} 
  read.table(file=input$file$datapath, header =TRUE, sep=",") 
})

output$X = renderUI({ 
    selectInput("X", "Select field to plot along X axis", names(lastgang()), selected = NULL)
})

output$Y = renderUI({ 
    selectInput("Y", "Select field to plot along Y axis", names(lastgang()), selected = NULL)
})

output$plot <- renderPlot({ 
   if (is.null(input$X) || is.null(input$Y)){return()} 
   x = input$X
   y = input$Y
   plot(as.numeric(lastgang()$x),as.numeric(lastgang()$y))    
  })
})

ui.R

   library(shiny)

shinyUI(fluidPage(

 titlePanel("Source Design"),
 sidebarLayout(
  sidebarPanel(fileInput("file", label = h4("Select *.csv file")),

             uiOutput("X"),
             uiOutput("Y"),
             submitButton("Plot")
),

mainPanel(
  plotOutput('plot')  )
)
))

Hard to tell while having no glue how your data looks like. I agree the conversion as.numeric probably produces a vector which only consists of NA entries. What kind of data do you have? Edit: I saw you call x <- input$X and afterwards you are calling lastgang()$x. That ought to be only x, or not? Otherwise the assignment x <- input$X makes no sense I think. Unfortunately I have no experience with shiny... — FlorianSchunke
x = input$X will return a column/element name. To get the series of values under that column i am calling lastgang()$x where lastgang() is bascially a R dataframe converted from .csv file. Further i checked that both columns that i have selected are of type num . — Jio

FlorianSchunke FlorianSchunke · Accepted Answer · 2016-08-09T12:43:32

If x and y are strings and lastgang is a dataframe. Then your error does not have any to do with the use of shiny. The following do not work in R

> D <- data.frame(Col1=1:5, Col2=11:15)
> a <- 'Col1'
> b <- D$a
> b
NULL

This is because after $ R expects a column name of the data frame. If the variable before $ is a data frame, then you got NULL if the column name does not exist. You want the column called Col1

> D <- data.frame(Col1=1:5, Col2=11:15)
> a <- 'Col1'
> b <- D[, which(names(D) == a)]
> b
[1] 1 2 3 4 5

R shiny render UI does not work

1 Answers