How to access to columns in data frame uploaded in shiny app? - file-io

Question

I am trying to create a shiny app. This app uses a .csv file uploaded by the user. I do not really understand how fileInput() works in the sense of storing the data frame.
I am using this code to upload the file:
data_OBS = reactive({
inFile <- input$file1
if (is.null(inFile))
return(NULL)
read.csv(inFile$datapath, header=T, sep=",")
})
If I understood well, the data frame should be accesible in data_OBS(). If the .csv file I want to upload has a column named for example "CL" in normal R enviorement I should be able to access using data_OBS$CL. However, in shiny data_OBS() is a function. I have tried data_OBS$CL, data_OBS()$CL, data_OBS(CL) but none of them worked. How can access to the data just uploaded?
Thanks in advance,
Best,

Answer 1

You can access it with data_OBS()$CL, but only inside reactive context such as observe, observeEvent, eventReactive.
Here is a minimal example using observeEvent:
ui <- fluidPage(
fileInput("file1", "Choose CSV File"),
textOutput("text"),
actionButton("print", "Print to text output")
)
server <- function(input, output, session){
data_OBS = reactive({
inFile <- input$file1
if (is.null(inFile))
return(NULL)
read.csv(inFile$datapath, header=T, sep=",")
})
observeEvent(input$print, {
req(input$file1) # Doesn't do anything until a file is uploaded
output$text <- renderText(data_OBS()$CL)
})
}
shinyApp(ui, server)

Answer 2

First to check it did not return null. Also, you may force return(read.csv(...))
data_OBS()$CL should work.