Uploading CSV Files to Shiny Apps with Reactive Datasets

Understanding the Problem and Solution

As a beginner in R-shiny apps, you’re facing a common challenge: how to plot an uploaded dataset using shiny. In this article, we’ll delve into the world of shiny app development, exploring the intricacies of file uploads, reactive datasets, and rendering plots.

The question at hand involves two files: server.R and ui.R. The former contains the server-side logic for the application, while the latter defines the user interface. Our goal is to create a functional R-shiny app that allows users to upload a CSV file, select columns for plotting, and generate a scatterplot.

File Input and Reactive Datasets

To tackle this problem, we’ll employ the reactive function from shiny, which enables us to create reactive datasets. A reactive dataset is a function that returns an expression involving inputs, outputs, or other reactive expressions. In our case, we want to read the uploaded file, update the names of the data frame, and pass it to the render functions.

The solution involves two primary components:

File Input: We’ll use the fileInput function from shiny’s UI module to create a file input interface. This will allow users to select a CSV file.
Reactive Dataset: We’ll utilize the reactive function to create a reactive dataset that reads the uploaded file, updates inputs, and returns an expression involving these updated inputs.

Solution Overview

To implement this solution, we’ll:

Define the UI for the shiny app using ui.R.
Create a reactive dataset in server.R that reads the uploaded file, updates inputs, and returns an expression involving these updated inputs.
Use the reactive dataset to render plots.

Solution Implementation

Here’s the complete implementation:

library(shiny)
library(datasets)

## Define UI for application
ui <- shinyUI(fluidPage(
  titlePanel("Column Plot"),
  tabsetPanel(
    tabPanel("Upload File",
             titlePanel("Uploading Files"),
             sidebarLayout(
               sidebarPanel(
                 fileInput('file1', 'Choose CSV File',
                           accept=c('text/csv', 
                                    'text/comma-separated-values,text/plain', 
                                    '.csv')),

                 # added interface for uploading data from
                 # http://shiny.rstudio.com/gallery/file-upload.html
                 tags$br(),
                 checkboxInput('header', 'Header', TRUE),
                 radioButtons('sep', 'Separator',
                              c(Comma=',',
                                Semicolon=';',
                                Tab='\t'),
                              ','),
                 radioButtons('quote', 'Quote',
                              c(None='',
                                'Double Quote'='"',
                                'Single Quote'="'"),
                              '"')

               ),
               mainPanel(
                 tableOutput('contents')
               )
             )
    ),
    tabPanel("First Type",
             pageWithSidebar(
               headerPanel('My First Plot'),
               sidebarPanel(

                 # "Empty inputs" - they will be updated after the data is uploaded
                 selectInput('xcol', 'X Variable', ""),
                 selectInput('ycol', 'Y Variable', "", selected = "")

               ),
               mainPanel(
                 plotOutput('MyPlot')
               )
             )
    )

  )
))

## Define server logic for application
server <- shinyServer(function(input, output, session) {
  # added "session" because updateSelectInput requires it


  data <- reactive({
    req(input$file1) ## ?req #  require that the input is available

    inFile <- input$file1 

    # tested with a following dataset: write.csv(mtcars, "mtcars.csv")
    # and                              write.csv(iris, "iris.csv")
    df <- read.csv(inFile$datapath, header = input$header, sep = input$sep,
                     quote = input$quote)


    # Update inputs (you could create an observer with both updateSel...)
    # You can also constraint your choices. If you wanted select only numeric
    # variables you could set "choices = sapply(df, is.numeric)"
    # It depends on what do you want to do later on.

    updateSelectInput(session, inputId = 'xcol', label = 'X Variable',
                      choices = names(df), selected = names(df))
    updateSelectInput(session, inputId = 'ycol', label = 'Y Variable',
                      choices = names(df), selected = names(df)[2])

    return(df)
  })

  output$contents <- renderTable({
      data()
  })

  output$MyPlot <- renderPlot({
    # Correct way:
    x <- data()[, input$xcol]
    plot(x)

  })
})

# Run the application 
shinyApp(ui = ui, server = server)

Conclusion

In this article, we explored how to create a shiny app that allows users to upload a CSV file and generates a scatterplot. We utilized the reactive function from shiny’s server-side logic module to create reactive datasets. This enables us to read uploaded files, update inputs, and return expressions involving these updated inputs.

The final solution involves defining UI for the application using ui.R, creating a reactive dataset in server.R, and rendering plots using the reactive dataset.

Last modified on 2023-12-21