why does the missing function not work inside of reactive RShiny? - r

Question

I have an R shiny app that filters on some variables and returns a table using modules. I'd like to use missing() so that the app will still work even if no value is provided to the module. However, when I use missing() inside reactive() it gives an error: Warning: Error in missing: 'missing' can only be used for arguments. Does anyone know why this might be the case? Is there a way to get around this?
Example app:
df <- data.frame(a = sample(letters,100,T), b = sample(10,100,T))
dfFilter <- function(data, a, b){
if (!missing(a)) {
if(!is.null(a)){
data <- data[data$a %in% a,]
}
}
if (!missing(b)) {
if(!is.null(b)){
data <- data[data$b %in% b,]
}
}
return(data)
}
filterTable <- function(input, output, session, data, aFetcher, bFetcher){
return(reactive(dfFilter(data = data,
a = switch(!missing(aFetcher),
aFetcher(),NULL),
b = switch(!missing(bFetcher),
bFetcher(), NULL))))
}
displayTableUI <- function(id){
ns <- NS(id)
DT::dataTableOutput(ns('displayer'))
}
displayTable <- function(input, output, session, data){
output$displayer <- DT::renderDataTable(data())
}
chooserUI <- function(id){
ns <- NS(id)
uiOutput(ns('filter'))
}
chooseA <- function(input, output, session, data){
output$filter <- renderUI({
ns <- session$ns
pickerInput(inputId = ns('filter'),
label = 'Choose A:',
choices = unique(data$a),
options = list(`actions-box` = TRUE),
multiple = TRUE)
})
return(reactive(input$filter))
}
chooseB <- function(input, output, session, data){
output$filter <- renderUI({
ns <- session$ns
pickerInput(inputId = ns('filter'),
label = 'Choose B:',
choices = unique(data$b),
options = list(`actions-box` = TRUE),
multiple = TRUE)
})
return(reactive(input$filter))
}
ui <- fluidPage(
tabPanel('data',
sidebarPanel(
chooserUI('aChooser'),
chooserUI('bChooser')
),
mainPanel(
displayTableUI('table1')
)
)
)
server <- function(input,output){
chosenA <- callModule(chooseA,
id = 'aChooser',
data = df)
chosenB <- callModule(chooseB,
id = 'bChooser',
data = df)
table1 <- callModule(filterTable,
data = df,
id = 'tableFilterer',
aFetcher = chosenA,
bFetcher = chosenB)
callModule(displayTable, id = 'table1', data = table1)
}
shinyApp(ui, server)

Answer 1

Fixed by using exists() instead of !missing():
df <- data.frame(a = sample(letters,100,T), b = sample(10,100,T))
dfFilter <- function(data, a, b){
if (!missing(a)) {
if(!is.null(a)){
data <- data[data$a %in% a,]
}
}
if (!missing(b)) {
if(!is.null(b)){
data <- data[data$b %in% b,]
}
}
return(data)
}
filterTable <- function(input, output, session, data, aFetcher, bFetcher){
return(reactive(dfFilter(data = data,
a = switch(exists(aFetcher),
aFetcher(),NULL),
b = switch(exists(bFetcher),
bFetcher(), NULL))))
}
displayTableUI <- function(id){
ns <- NS(id)
DT::dataTableOutput(ns('displayer'))
}
displayTable <- function(input, output, session, data){
output$displayer <- DT::renderDataTable(data())
}
chooserUI <- function(id){
ns <- NS(id)
uiOutput(ns('filter'))
}
chooseA <- function(input, output, session, data){
output$filter <- renderUI({
ns <- session$ns
pickerInput(inputId = ns('filter'),
label = 'Choose A:',
choices = unique(data$a),
options = list(`actions-box` = TRUE),
multiple = TRUE)
})
return(reactive(input$filter))
}
chooseB <- function(input, output, session, data){
output$filter <- renderUI({
ns <- session$ns
pickerInput(inputId = ns('filter'),
label = 'Choose B:',
choices = unique(data$b),
options = list(`actions-box` = TRUE),
multiple = TRUE)
})
return(reactive(input$filter))
}
ui <- fluidPage(
tabPanel('data',
sidebarPanel(
chooserUI('aChooser'),
chooserUI('bChooser')
),
mainPanel(
displayTableUI('table1')
)
)
)
server <- function(input,output){
chosenA <- callModule(chooseA,
id = 'aChooser',
data = df)
chosenB <- callModule(chooseB,
id = 'bChooser',
data = df)
table1 <- callModule(filterTable,
data = df,
id = 'tableFilterer',
aFetcher = chosenA,
bFetcher = chosenB)
callModule(displayTable, id = 'table1', data = table1)
}
shinyApp(ui, server)