Call Variable from reactive data() in R Shiny App

Question

I would like to call a certain variable within a reactive expression. Something like this:

server.R

library(raster)

shinyServer(function(input, output) {

data <- reactive({
inFile <- input$test #Some uploaded ASCII file
asc <- raster(inFile$datapath) #Reads in the ASCII as raster layer

#Some calculations with 'asc':

asc_new1 <- 1/asc
asc_new2 <- asc * 100
})

output$Plot <- renderPlot({

inFile <- input$test
if (is.null(inFile)
 return (plot(data()$asc_new1)) #here I want to call asc_new1
plot(data()$asc_new2)) #here I want to call asc_new2
})
})

Unfortunately I could't find out how to call asc_new1 and asc_new2 within data(). This one doesn't work:

data()$asc_new1

Ciarán Tobin · Accepted Answer · 2013-07-02 14:17:24Z

11

Reactives are just like other functions in R. You can't do this:

f <- function() {
  x <- 1
  y <- 2
}

f()$x

So what you're within output$Plot() won't work either. You can do what you want by returning a list from data().

data <- reactive({

  inFile <- input$test 
  asc <- raster(inFile$datapath) 
  list(asc_new1 = 1/asc, asc_new2 = asc * 100)

})

Now you can do:

data()$asc_new1

answered Jul 2, 2013 at 14:17

Ciarán Tobin

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2 Comments

viktor_r Over a year ago

For some reason I still get the same Error. I've putted my variabale into a list but I still can't call it: Error in data()$fitnew : $ operator not defined for this S4 class

Ciarán Tobin Over a year ago

Are you definitely putting the list on the last line of your data() function? This is what will get returned.

four-eyes · Accepted Answer · 2015-09-30 17:19:33Z

0

"With data()$asc_new1 you wont be able to access the in the reactive context created variables (at least with the current shiny version). You need data()[1] data()[2] if you put it in a list like MadScone. Calling it with the $ sign would raise

Warning: Unhandled error in observer: $ operator is invalid for atomic vectors

However, the error your getting

Error in data()$fitnew : $ operator not defined for this S4 class

is not only because you access the variable wrong. You named the output of your reactive function data which is reserved name in R. You want to change that to myData or something.

answered Sep 30, 2015 at 17:19

four-eyes

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