Stepping Up the Problem

Obviously, we are all shiny experts by now. The previous walk through gave us a crash course on how to layout an app, how to provide static elements like text and images, and finally how to deal with reactive events by setting up an observer.

A logical next step might be how to construct an app that not only responds to user-defined information, but different types of user information.

Let’s build an app that takes a csv file, allows the user to preview the data file that was read in, select two numeric variables, and plot those against each other. This seems like quite an easy task, given what we just accomplished before, but when we break down the step-by-step issues it is quite complex.

Disclosure: Most of this app was scavenged from parts of the File Upload tutorial, and this stackoverflow problem on reactive data sets.

The Problem(s)

An in-depth walk through of this issue is beyond the scope of this tutorial, but let me highlight some of the new issues that this problem brings to a coder’s attention.

1). Upload an external .csv file

2). Preview uploaded file as data frame

3). Select two numeric variables

4). Plot user-selected variables

The Solution

You can see this app running on shinyapps.io

library(shiny)
library(ggplot2)

ui <- fluidPage(
  titlePanel("File Upload and Scatter Plot"),
  tabsetPanel(
    
    ## First tab
    tabPanel("Upload File",
             
             ## A sidebar layout within the first tab
             sidebarLayout(
               
               ## left sidebar gets this:
               sidebarPanel(
                 fileInput('file1', 'Choose CSV File',
                           accept=c('text/csv', 
                                    'text/comma-separated-values,text/plain', 
                                    '.csv')),
                 ## -----
                 tags$br(),
                 ## -----
                 
                 ## Some values for how to read in the file
                 checkboxInput('header', 'Header', TRUE),
                 radioButtons('sep', 'Separator',
                              c(Comma=',',
                                Semicolon=';',
                                Tab='\t'),
                              ',')
               ),
               
               ## Main panel gets this:
               mainPanel(
                 tableOutput('contents')
               )
             )
    ),
    
    ## Second tab
    tabPanel("Scatter Plot",
             sidebarLayout(
               sidebarPanel(
                 
                 selectInput('xcol', 'X Variable', ""),
                 selectInput('ycol', 'Y Variable', "", selected = "")
                 
               ),
               mainPanel(
                 plotOutput('MyPlot')
               )
             )
    )
    
  )
)

server <- function(input, output, session) {
  # added "session" because updateSelectInput requires it
  
  data <- reactive({ 
    req(input$file1) 
    
    inFile <- input$file1 

    df <- read.csv(inFile$datapath, header = input$header, sep = input$sep)
  
    updateSelectInput(session, inputId = 'xcol', label = 'X Variable', choices = names(df),
                      selected = names(df)[sapply(df, is.numeric)])
    updateSelectInput(session, inputId = 'ycol', label = 'Y Variable', choices = names(df),
                      selected = names(df)[sapply(df, is.numeric)])
    
    return(df)
  })
  
  output$contents <- renderTable({
    head(data(), 10)
  })
  
  output$MyPlot <- renderPlot({
    
    x <- data()[, input$xcol]
    y <- data()[, input$ycol]
    newdf <- as.data.frame(cbind(x,y))
    
    ggplot(newdf, aes(x, y)) +
      geom_point() +
      xlab(as.character(input$xcol)) +
      ylab(as.character(input$ycol)) +
      stat_smooth(method = 'lm') +
      theme_bw(base_size = 15)
    
  })
}

shinyApp(ui, server)

If your itch for shiny tutorials still isn’t complete, check out how to use the shiny package for collecting surveys with this simple survey app. You can also check out the resource page for more tutorials and how to extend shiny.

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