Producing PDF report using knitr (LaTeX) from Shiny application

Question

I am trying to create a shiny application that will allow you to download a nicely formatted PDF report, according to user-defined sub-analyses. I found this gist containing a minimal example, which works just fine. However, when I tried to add a plot, based on the 'Miles-per-gallon' example from the Rstudio gallery, I ran into some errors when I tried adapting the code.

Here is my server.R code:

library(knitr) library(datasets) library(ggplot2)  mpgData <- mtcars mpgData$am <- factor(mpgData$am, labels = c("Automatic", "Manual"))  shinyServer(function(input, output) { formulaText <- reactive({     paste("mpg ~", input$variable) })  # Return the formula text for printing as a caption output$caption <- renderText({     formulaText() })  # Generate a plot of the requested variable against mpg and only  # include outliers if requested output$mpgPlot <- renderPlot({     boxplot(as.formula(formulaText()),              data = mpgData,             outline = input$outliers) })  myPlot1 <- reactive({     p <- print(ggplot(mpgData, aes(mpg, input$variable)) +     geom_line()) })   myPlot2 <- reactive({      #renderPlot({      p <- print(          boxplot(as.formula(formulaText()),                   data = mpgData,                  outline = input$outliers)      )  })  output$report = downloadHandler(     filename = 'myreport.pdf',     content = function(file) {         out = knit2pdf('input.Rnw', clean = TRUE)         file.rename(out, file) # move pdf to file for downloading     },     contentType = 'application/pdf' ) }) 

and here is my ui.r code

library(shiny) library(datasets)  shinyUI(fluidPage(  # Application title titlePanel("Miles Per Gallon"),  # Sidebar with controls to select the variable to plot against mpg # and to specify whether outliers should be included sidebarLayout(     sidebarPanel(         textInput('firstname', 'First name', value = 'Adam'),         textInput('lastname', 'Last name', value = 'Smith'),         downloadButton('report'),          selectInput("variable", "Variable:",                     c("Cylinders" = "cyl",                       "Transmission" = "am",                       "Gears" = "gear")),          checkboxInput("outliers", "Show outliers", FALSE)     ),      # Show the caption and plot of the requested variable against mpg     mainPanel(         h3(textOutput("caption")),          plotOutput("mpgPlot")      ) ) )) 

while the input.Rnw file looks like this:

\documentclass{article}  \begin{document}  <<names>>= input$firstname input$lastname @  <<>>= #output$mpgPlot ## N.B. This threw an error! Cannot call an object like this from shiny print(myPlot1()) @  <<>>= print(myPlot2()) @  \end{document} 

I've been playing around with this for a few hours now, and I'm pretty stuck. The input$names part works fine, but I cannot figure out how to bring in a reactive plot. The error/warning message is 'Error: object ’input’ not found', so I know it is not detecting the input$variable changes being passed from the ui.R script. Thanks for your help solving this

sessionInfo() R version 3.1.0 (2014-04-10) Platform: x86_64-apple-darwin13.1.0 (64-bit)  locale: [1] en_GB.UTF-8/en_GB.UTF-8/en_GB.UTF-8/C/en_GB.UTF-8/en_GB.UTF-8  attached base packages: [1] stats     graphics  grDevices utils     datasets  methods   base       other attached packages: [1] ggplot2_0.9.3.1.99 knitr_1.6          shiny_0.10.0        loaded via a namespace (and not attached):  [1] bitops_1.0-6       caTools_1.17       colorspace_1.2-4   digest_0.6.4       evaluate_0.5.5     formatR_0.10       grid_3.1.0         gtable_0.1.2        [9] highr_0.3          htmltools_0.2.4    httpuv_1.3.0       labeling_0.2       MASS_7.3-33        munsell_0.4.2      plyr_1.8.1         proto_0.3-10       [17] RColorBrewer_1.0-5 Rcpp_0.11.2        reshape2_1.4       RJSONIO_1.2-0.2    scales_0.2.4       stringr_0.6.2      tools_3.1.0        xtable_1.7-3 

Answer 1

As suggested in my comment, you should use aes_string() to programmatically pass in arguments into ggplot. The error you are getting is because 'input' is a character value while aes() expects unquoted names. Here is how you should replace the call to aes(mpg, input$variable):

myPlot1 <- reactive({     p <- print(ggplot(mpgData, aes_string('mpg', input$variable)) +     geom_line()) })