list of values for selectInput - user-interface

Question

I want to create a "selectInput" widget for which the choices of values are the names of columns in a dataset imported by a "fileInput" widget.
I tried to "tableOutput" the names of the dataset, as an argument to the "choices" parameters of the "selectInput" widget, but it doesn't work. The only choices I get in the widget are "name", "id" and "class".
Here's the code I used:
library(shiny)
ui <- fluidPage(
# Widget for loading data set
fileInput("file", label = h4("Input csv data set")),
# Widget for selecting the variable among names of columns of the data set
selectInput("select.variable", label = h4("Select variable from data set"),
choices = tableOutput("list.var"), selected = 1) # This approach doesn't work
)
server <- function(input, output) {
# The goal was to get the list of names of columns to use it as "choices"
# in the "selectInput" widget
output$list.var <- renderTable({
inFile <- input$file
if (is.null(inFile)) # To avoid error messages when the file is not yet loaded
return(NULL)
# After the file is loaded
data.fr <- read.csv(inFile$datapath)
list.var <- names(data.fr[1,]) # Get the names of the columns of the dataset
})
}
shinyApp(ui = ui, server = server)
Is there a way to use the names of columns of an imported dataset as choices for a "selectInput" widget?

Answer 1

Something like this should do the trick. I used renderUI to create the slider widget from your dataset
library(shiny)
ui <- fluidPage(
# Widget for loading data set
fileInput("file", label = h4("Input csv data set")),
uiOutput("myslider")
)
server <- function(input, output) {
# The goal was to get the list of names of columns to use it as "choices"
# in the "selectInput" widget
output$myslider <- renderUI({
# Widget for selecting the variable among names of columns of the data set
selectInput("select.variable", label = h4("Select variable from data set"),
choices = names(mydata()), selected = 1) # This approach doesn't work
})
mydata <- reactive({
inFile <- input$file
if (is.null(inFile)) # To avoid error messages when the file is not yet loaded
return(NULL)
# After the file is loaded
data.fr <- read.csv(inFile$datapath)
names(data.fr[1,]) # Get the names of the columns of the dataset
})
output$list.var <- renderTable({
mydata()
})
}
shinyApp(ui = ui, server = server)