CODEWITHSUNDEEP
rshinydplyrreactive
user259933
user259933

Reputation: 33

Trouble using inputted variable with dplyr in Shiny with a reactive dataset

I have browsed the other answers regarding issues with plyr and dplyr without success.

I want to use two inputted variables in the dplyr "group_by_" and "summarise" commands. I can not seem to find the right syntax to input my variable into summarise to get a mean with the grouping. Turning it back into a data frame doesn't work.

new_frame <- frame() 
new_frame[[input$ycol]]

sapply gives a result but it ignores the grouping levels and gives me the mean of the entire column.

mean = sapply(frame()[input$ycol],mean)

I am not sure what other options to use.

MWE with error as follows.

library(shiny)
ui <- fluidPage(

   titlePanel("MWE using faithful data"),
   sidebarLayout(
      sidebarPanel(
        selectInput('xcol', 'X Variable', "",choices = "colour"),
        selectInput('ycol', 'Y Variable', "",choices = c("waiting", "eruptions"))),

      mainPanel(
         tableOutput("distPlot"))))

server <- function(input, output) {

  frame <- reactive({

    faithful <- faithful %>% mutate(colour = rep(c("red","white"),136))
    return(faithful)
  })

   output$distPlot <- renderTable({
     frame() %>% group_by_(input$xcol) %>% 
       summarise(mean = mean(input$ycol))
   })
}
shinyApp(ui = ui, server = server)

If I hard code the line 

summarise(mean = mean(input$ycol))

to

summarise(mean = mean(eruptions))

Using summarise_ is no good either.

it gives me what I want, but that is not an option in my actual code. Any help would be appreciated.

Thanks

Upvotes: 2

Views: 1571

Answers (1)

akrun
akrun

Reputation: 887961

The main problem is how we are evaluating the input$xcol and input$ycol. These are string elements. One option is to convert it to symbol with rlang::sym and evalute with !!

library(shiny)
library(dplyr)
ui <- fluidPage(

  titlePanel("MWE using faithful data"),
  sidebarLayout(
    sidebarPanel(
      selectInput('xcol', 'X Variable', "",choices = "colour"),
      selectInput('ycol', 'Y Variable', "",choices = c("waiting", "eruptions"))),

    mainPanel(
      tableOutput("distPlot"))))

server <- function(input, output) {

  frame <- reactive({

  faithful %>%
           mutate(colour = rep(c("red","white"),136))

  })

  output$distPlot <- renderTable({
       frame() %>%
            group_by(!! rlang::sym(input$xcol)) %>% 
            summarise(mean = mean(!! rlang::sym(input$ycol)))
  })
}
shinyApp(ui = ui, server = server)

-output

enter image description here

Upvotes: 3

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