Passing column name via selectInput in shiny application

问题

I have a simple shiny app, I would like to pass the value from the selectInput as a column name of data frame and use it in ggplot. My UI code looks like that:

library(shiny)

# Define UI for application that draws a histogram
shinyUI(fluidPage(

  # Application title
  titlePanel("Title"),

  # Sidebar with a slider input for the number of bins
  sidebarLayout(
    sidebarPanel(
      selectInput(inputId = "yaxis", 
                  label = "Y-axis",
                  choices = list("Overall Rank" = "overall_rank", 
                                 "Income Deprivation" = "income_deprivation_rank"), 
                  selected = "income_deprivation_rank"),

      selectInput(inputId = "xaxis", 
                  label = "X-axis",
                  choices = list("Overall Rank" = "overall_rank", 
                                 "Income Deprivation" = "income_deprivation_rank"), 
                  selected = "overall_rank")),

    # Show a plot of the generated distribution
    mainPanel(
      plotOutput("distPlot"),
      h5("Notes"),
      p("notes")
    )
      )
    ))

My server side code is vary simple, I have a SPARQL query (cut here to save the space) that creates simple data frame:

# Libs
require(shiny); require(SPARQL); require(ggplot2)

# Server function
shinyServer(function(input, output) {

  # Source the data

  ## Define endpoint URL.
  endpoint <- "http://data.opendatascotland.org/sparql.csv"

  ### Create Query 
  query.simd <- "PREFIX stats: <http://statistics.data.gov.uk/id/statistical-geography/>
      (...) cut to save space (...)"

  ## Make the data
  dta.simd<- SPARQL(url = endpoint, query = query.simd, format = "csv")$results


  ## Make the plot
  output$distPlot <- renderPlot({

    xaxis <- as.character(input$xaxis) 
    yaxis <- as.character(input$yaxis)

    # draw the the plot
    ggplot(data = dta.simd, aes(x = xaxis, y = yaxis)) +
      geom_point(shape=1)

})
})

The query results in a simple data frame, resambling the extract below:

observation overall_rank income_deprivation_rank
a001        2            6
a002        10           7
a003        11           9

After compiling the app I keep on receiving the Error: object 'xaxis' not found. This leads me to believe that for whatever reason the value from the input$xaxis is not passes to the xaxis object and cannot be used in ggplot. If I decide to replace the as.character(input$yaxis) with a string corresponding to the column name, like for instance overall_rank and the other one income_deprivation_rank the app works as it should, so the problem is clearly associated with using the input$xaxis value. I tried the code with no as.character() function but got the same error message.

回答1:

Wherever you would normally reference the column name as a string like input$colName, replace it with get(input$colName). This way Shiny knows to fetch the value of input$colName instead of treating it as a string.

来源：https://stackoverflow.com/questions/26701775/passing-column-name-via-selectinput-in-shiny-application

标签

input

dataframe

Shiny