passing on data from observe function to download - r

Question

I got stuck on my first shiny app again. So far the App was runing fine, but now I wanted to download the plot I generated and I can not work out how to get the results out of the observe function.
As I can not generate the plot outside the observe function, I was thinking I would assign the necessary data to a global variable useing <<-, but if I run a reactive function e.g. df.selected.columns() this seem to cause errors.
Can someone give me a hint how to proceed?
Thank you so much for any suggestions! Aishe
Here is me code:
ui <- shinyServer(
fluidPage(
tabsetPanel(
tabPanel("Data upload",
titlePanel("Data upload"),
sidebarLayout(
sidebarPanel(
fileInput("file1", "Choose CSV File",multiple = TRUE, accept = c("text/csv","text/comma-separated-values,text/plain",".csv")),
tags$hr(),
checkboxInput("header", "Header", TRUE), radioButtons("sep", "Separator", choices = c(Comma = ",", Semicolon = ";",Tab = "\t"), selected = ","),
tags$hr(),
checkboxInput("disp", "Display",TRUE),
tags$hr(),
uiOutput("choose_first_column"),
uiOutput("choose_second_column"),
br()
),
mainPanel(
tableOutput("contents"),
tags$hr(),
tableOutput("tab"),
tags$hr(),
uiOutput("download"),
plotOutput("headplot")
)
)
),
tabPanel("2","2"
)
)
)
)
server <- shinyServer(
function(input, output) {
observe({
req(input$file1)
df <- read.csv(input$file1$datapath,
header = input$header,
sep = input$sep,
quote = input$quote)
output$contents <- renderTable({
(head(df))})
output$choose_first_column <- renderUI({
colnames <- names(df)
selectInput("column_1", "Choose Date column",
choices = colnames,
selected = colnames)})
output$choose_second_column <- renderUI({
colnames <- names(df)
selectInput("column_2", "Choose Variable column",
choices = colnames,
selected = colnames)})
df.selected.columns <- reactive({
df.columns <- df[,c(input$column_1,input$column_2)]
return(df.columns)
})
output$tab <- renderTable({
(head(df.selected.columns()))
})
Plot1 <- reactive({
plot(head(df.selected.columns()[,2]))
})
output$headplot <- renderPlot({
Plot1()
})
# This comes closest to what I wanted to do. However, now I can not select the columns anymore.
# try(result <<- head(df.selected.columns()[,2]),silent=T)
# With this line it crushes straight away
# result <<- head(df.selected.columns()[,2])
})
output$download <- renderUI({
if(!is.null(input$column_1) & !is.null(input$column_2)) {
downloadButton('OutputPlot', 'Download Plot')
}
})
output$OutputPlot <- downloadHandler(
filename = function() {
paste('plot', '.pdf', sep='')
},
content=function(file){
pdf(file)
plot(result)
dev.off()
})
})
runApp(list(ui = ui, server = server))
Input data example:
date time level
01.01.2000 00:00:00 0.3724
01.01.2000 01:00:00 0.192
01.01.2000 02:00:00 -0.0252

Answer 1

Remove the observe
Make the loaded file a reactive
Update all references to df to df() since it's now a reactive expression
Add appropriate req() functions to prevent error messages
In your downloadHandler you have plot(result), but there's no such thing as result. You want Plot() or plot(df.selected.columns())
You should be confirming that your selected delimiter is actually splitting the loaded table correctly before your return the loaded table. Without that, you'll get errors and strange results/
Here's the updated df and downloadHandler functions to get you started:
df <- reactive({
req(input$file1)
read.csv(input$file1$datapath,
header = input$header,
sep = input$sep,
quote = input$quote)
})
output$OutputPlot <- downloadHandler(
filename = function() {
paste('plot', '.pdf', sep='')
},
content=function(file){
pdf(file)
plot(head(df.selected.columns()[,2]))
dev.off()
})