Force no default selection in selectInput() - r

Question

The Shiny documentation mentions that for selectInput():
selected The value (or, if none was supplied, the title) of the navigation item that should be selected by default. If NULL, the first navigation will be selected.
What if by default I don't want to select any value from select list?
Actually my select value is getting selected by default and rest part of app is getting executed automatically. But I don't want to select any value initially. What should I supply to the selected argument in selectInput() to do that?
Indeed, I don't want anything to be selected automatically. I used the code below but still it's selecting first available value from the list. I want there to be no selection by default, so the user can then select any option.
output$Choose_App <- renderUI({
selectInput("app",
"Select App:",
choices = as.character(mtrl_name),
selected = NULL ,
multiple = FALSE
)
})
Going through the documentation I noticed that the selection can be empty only if I select multiple=TRUE. Is this correct?
When I changed to multiple=TRUE, then it it's not getting selected by default, which is what I want. But unfortunately before making any selection I am also getting following error message:
ERROR: bad 'file' argument
Does anybody know about this if I am doing something wrong? But if I select this file then error is gone.
I am using following code for this:
# server.R
setwd("/opt/shiny-server/samples/sample-apps/P-Dict_RDS2")
mtrl_name <- try(system("ls | grep -i .rds", intern = TRUE))
shinyServer(function(input, output) {
# First UI input (Service column) filter clientData
output$Choose_Molecule <- renderUI({
selectInput("molecule",
"Select Molecule:",
choices = as.character(mtrl_name),
selected = input$molecule,
multiple = TRUE
)
})

Answer 1

You can use the selectize input instead of the select input, with some custom selectize options to set the initial selection to be empty. An example has been provided in the Shiny Gallery. In particular, see the example #6.
# make sure you have shiny >= 0.9.1
selectizeInput(
'e6', '6. Placeholder', choices = state.name,
options = list(
placeholder = 'Please select an option below',
onInitialize = I('function() { this.setValue(""); }')
)
)
BTW, for the error "ERROR: bad 'file' argument", I do not think anybody can help you without seeing the source code of your app, and it may be a separate question.

Answer 2

Faced a similar issue. The solution I found is based of #MKa's answer. You do not want to set multiple=T if your code can't handle multiple values. What I suggest is:
selectInput("molecule",
"Select Molecule:",
choices = c("",as.character(mtrl_name)),
selected = NULL,
multiple = F
)
And to retrieve the value selected:
if(!is.null(input$molecule))
{
if(nchar(input$molecule)>1)
{
#do your thing..
}
}
Fixed my problem. Let me know if you found a better solution.

Answer 3

I think you can get around it by adding an empty string to your choice list:
selectInput("app",
"Select App:",
choices = c("", as.character(mtrl_name)),
selected = NULL,
multiple = FALSE)

Answer 4

#Yihui Xie's answer requires selectInput(..., selectize = TRUE). If you want selectize = FALSE, you can still achieve a similar effect as follows.
This is not documented:
selected The initially selected value (or multiple values if multiple = TRUE). If not specified then defaults to the first value for single-select lists and no values for multiple select lists.
But for single-select lists if you can use selectize = FALSE, size = 4 (any non-NULL size would work), then you can set selected = FALSE to force no default selection.
library(shiny)
# Define UI for application that draws a histogram
ui <- fluidPage(
mainPanel(
uiOutput("Choose_Molecule")
)
)
# Define server logic required to draw a histogram
server <- function(input, output) {
# First UI input (Service column) filter clientData
output$Choose_Molecule <- renderUI({
selectInput("molecule",
"Select Molecule:",
choices = rownames(mtcars),
selected = FALSE,
multiple = FALSE
, selectize = FALSE, size = 4 ##needed for `selected = FALSE` to work
)
})
}
# Run the application
shinyApp(ui = ui, server = server)

Answer 5

A cleaner solution is to use selectizeInput, allow multiple selections, but then limit the maximum number of selections to 1. This means the default selection will be NULL, the user can only select 1 option, and you don't have to add an empty string to your choices or similar workarounds previously listed here.
selectizeInput(
"tag",
"Label",
choices = choices,
multiple = TRUE,
options = list(maxItems = 1)
)

Answer 6

A workaround would be to use updateSelectInput. The point here is that you set your selected = argument to length(your_vector_with_choices).
You can create a reactiveValues if you want your selectInput to be updated at the very beginning (in that case only observed at program start).
library(shiny)
shinyApp(
ui = fluidPage(
selectInput("state", "Choose a state:", NULL),
textOutput("result")
),
server = function(input, output, session) {
values <- reactiveValues(start = NULL)
observe({
choiceList <- list(`East Coast` = list("NY", "NJ", "CT"),
`West Coast` = list("WA", "OR", "CA"),
`Midwest` = list("MN", "WI", "IA"))
updateSelectInput(session, "state", choices = choiceList, selected = choiceList[length(choiceList)])
})
output$result <- renderText({
paste("You chose", input$state)
})
}
)

Answer 7

Answering after 6 years, as I got the same error now. We can write
selected = character(0)
to force not selecting any user input.

Answer 8

A modification of #rookieJoe answer is to use req() instead of the ifs. Read this page for an intro to the req() usage (in this specific question, the fact that req() takes the string "" as a "falsy" value).
For example, if the selectInput is like his:
selectInput("molecule",
"Select Molecule:",
choices = c("", as.character(mtrl_name)),
selected = NULL,
multiple = F
)
To retrive the value in a reactive as:
my_reactive <- reactive({
req(input$molecule)
# do your stuff
})