R Shiny selectInput returning error object 'input' not found

Question

I am trying to build a Shiny app that displays the output of a random forest in different tabs. Here, I only create a tab for the partial dependence plot to show the error I am receiving. Below is code for the global, server and ui files.

global.R

library(shiny)
setwd("C:/Users/rcaldwe4/Documents/Monthly Topic/Stackoverflow")

df <- data.frame(x1=sample(1:100,10000,replace=T),
                 x2=sample(1:100,10000,replace=T),
                 x3=sample(1:100,10000,replace=T),
                 y=as.factor(sample(0:1,10000,replace=T)))


train_x <- df[1:5000,-4]
train_y <- df[1:5000,4]
train1 <- data.frame(train_x,y=train_y)

test_x <- df[5001:10000,-4]
test_y <- df[5001:10000,4]

server.R

library(shiny)
library(randomForest)
library(AUC)
library(rpart)
library(lift)

#Define server logic required to output Random Forest
shinyServer(function(input,output){

  rfInput <- reactive({
    randomForest(x=train_x,y=train_y,importance=T,ntree=input$trees,keep.forest = T)
  })

  output$partDep <- renderPlot({
    partialPlot(x=rfInput(), pred.data=train1, x.var=input$select_var, which.class=1)
  })

})

ui.R

library(shiny)

shinyUI(
  fluidPage(
    titlePanel("Random Forest"),
    sidebarLayout(
      sidebarPanel(
        sliderInput("trees",
                    "Number of trees:",
                    min=0,
                    max=1000,
                    value=100,
                    step=50),
        selectInput("select_var", 
                    label = h4("Select variable for partial dependence plot"),
                    choices = names(train1)[1:3], 
                    selected = names(train1)[1])
      ),
      mainPanel(
        tabsetPanel(
          tabPanel("Dependence",
                   plotOutput("partDep"))
        )
      )
    )
  ))

The slider input for the number of trees to build is working fine. But, when I try to have the user select the variable for the partial dependence plot, I get this error:

Warning: Error in eval: object 'input' not found

I am not clear as to what the issue is with 'input'. I am wondering if it is an issue with using 'input' with the partialPlot function. Any suggestions would be great.

cdeterman cdeterman · Accepted Answer · 2016-04-20T15:27:08

This is a problem with partialPlot. This is addressed in another question here. The only explanation is that some plot functions use some non-standard evaluation.

If you change your partDep section in server.R to the following it works:

output$partDep <- renderPlot({
   do.call("partialPlot", 
           list(x=rfInput(), pred.data=train1, x.var = input$select_var, which.class = 1))
})

R Shiny selectInput returning error object 'input' not found

1 Answers