How to use workspace objects in an R Shiny application - r

Question

I would like a user to be able to type in the name of a dataframe object and have that object rendered as a formatted data table in a Shiny application.
Here is a toy example. There are two dataframe objects available in the workspace: df1 and df2. When the user types in df1, I would like that dataframe to be rendered. Likewise for df2 or for any other dataframe they have in their workspace.
I suspect I have to do something with environments or scoping or evaluation but I am not sure what.
I have commented in the code where I can hardcode in the built-in mtcars dataset and have that rendered correctly. Now I just want to be able to do the same for any ad-hoc dataframe in a user's workspace.
library(shiny)
set.seed(1234)
x <- sample.int(n = 20)
y <- sample(x = LETTERS, size = 20)
a <- rnorm(n = 20)
b <- sample(x = letters, size = 20)
df1 <- data.frame(x = x, y = y)
df2 <- data.frame(a = a, b = b)
# Define UI ----
ui <- fluidPage(
titlePanel("Using text inputs to select dataframes"),
sidebarLayout(position = "left",
sidebarPanel(width = 5,
textInput("dfInput", h5("Enter name of dataframe"),
value = "")),
mainPanel(width = 6,
h4("Here's your data"),
textOutput("selected_df"),
dataTableOutput("view")
)
)
)
# Define server logic ----
server <- function(input, output, session) {
output$selected_df <- renderText({
paste("You have selected ", input$dfInput)
})
output$view <-
renderDataTable({
input$dfInput # this should render the selected dataframe. If you replace this with mtcars then that dataset is correctly rendered.
})
}
# Run the app ----
shinyApp(ui = ui, server = server)

Answer 1

We are going to get all the dataframes within the global enviriment first and then use get in order to access the object. I changed the textInput to selectInput so you dont need to type anything, potentially making a mistake. Moreover I added the data from datasets package however you should build more test cases to check if the data exists
library(shiny)
set.seed(1234)
x <- sample.int(n = 20)
y <- sample(x = LETTERS, size = 20)
a <- rnorm(n = 20)
b <- sample(x = letters, size = 20)
df1 <- data.frame(x = x, y = y)
df2 <- data.frame(a = a, b = b)
mydataframes <- names(which(unlist(eapply(.GlobalEnv,is.data.frame))))
OpenData <- data()$results[,3]
#Define UI ----
ui <- fluidPage(
titlePanel("Using text inputs to select dataframes"),
sidebarLayout(position = "left",
sidebarPanel(width = 5,
selectInput("dfInput","Select Dataframe",
#choices = mydataframes,
list("Your Datasets" = c(mydataframes),
"R Datasets" = c(OpenData),
selected=NULL))),
mainPanel(width = 6,
h4("Here's your data"),
textOutput("selected_df"),
dataTableOutput("view")
)
)
)
# Define server logic ----
server <- function(input, output, session) {
output$selected_df <- renderText({
paste("You have selected ", input$dfInput)
})
output$view <-
renderDataTable({
as.data.frame(get(input$dfInput)) # this should render the selected dataframe. If you replace this with mtcars then that dataset is correctly rendered.
})
}
# Run the app ----
shinyApp(ui = ui, server = server)