Making ggvis plots reactive with shiny

Question

I have the following plot and I wish to make it interactive. More specifically, I'd like a slider for maximum supply to range between 60 and 120. I've read through the shiny and ggvis documentation and I can't get it to work. I've included an attempt below.

library(ggvis)
library(dplyr)
library(tidyr)

maximum_supply = input$maximum_supply

supply.function = function(supply)
  60 - 60/maximum_supply * supply

data_frame(quantity = 0:maximum_supply) %>%
  mutate(price = supply.function(quantity)) %>%
  ggvis(~quantity, ~price) %>%
  layer_lines()

shiny.R

library(shiny)
library(ggvis)
library(dplyr)

shinyServer(function(input, output) {

  reactive({ 
    maximum_supply = 120

    supply.function = function(supply)
      60 - 60/maximum_supply * supply

    data_frame(quantity = 0:maximum_supply) %>%
      mutate(price = supply.function(quantity)) %>%
      ggvis(~quantity, ~price) %>%
      layer_lines() %>%
      bind_shiny("ggvis", "ggvis_ui")
  })
})

ui.R

library(shiny)
library(ggvis)
library(dplyr)

shinyUI(fluidPage(

  titlePanel("Example"),

  sidebarLayout(
    sidebarPanel(
      sliderInput("maximum_supply",
                  "Maximum Supply",
                  min = 60,
                  max = 120,
                  value = 90),
    ),

    mainPanel(
      uiOutput("ggvis_ui"),
      ggvisOutput("ggvis")
    )
  )
))

Answer 1

Making the data that you pass to ggvis reactive is the key here, since you want to be able to subset it in response to user input. Also, the maximum_supply is part of input and can be accessed via input$maximum_supply in the supply function and the reactive data.

library(ggvis)
library(shiny)
library(dplyr)

shinyApp(
    shinyUI(fluidPage(
        titlePanel("Example"),
        sidebarLayout(
            sidebarPanel(
                sliderInput("maximum_supply",
                            "Maximum Supply",
                            min = 60,
                            max = 120,
                            value = 90),
                uiOutput("ggvis_ui")
            ),
            mainPanel(
                ggvisOutput("ggvis")
            )
        )
    )),
    shinyServer(function(input, output) {
        supply.function <- function(supply) {
            60 - 60/input$maximum_supply* supply
        }

        dat <- reactive({ data.frame( quantity = 0:input$maximum_supply ) })

        dat %>%
          mutate(price = supply.function(quantity)) %>%
          ggvis(~quantity, ~price) %>%
          layer_lines() %>%
          bind_shiny("ggvis", "ggvis_ui")
    })
)