R Shiny Application Error String Matching

Question

My goal with this shiny application is for people to be able to interactively match correct spellings of words to existing words. This is what I came up with so far which works and runs but it throws an error also. My question is, is there a better way to have the dropdown menu's formatted, how can I fix this error and also how can I then have the dataframe/table with users input saved after the fact.

Thanks!

The error:

Warning: Error in data.frame: arguments imply differing number of rows: 5, 0
  101: stop
  100: data.frame
   99: renderDataTable [#13]
   98: func
   85: renderFunc
   84: output$table
    3: runApp
    2: print.shiny.appobj
    1: <Anonymous>

The Code:



# Load Libraries
library(shiny)


words <- c("aapple", "apple", "bnanana", "pear", "banana")
choices = c("", "apple", "banana", "pear")

# Create User Interface
ui <- fluidPage(
  titlePanel("Matching Words with Dropdown Menus"),
  sidebarLayout(
    sidebarPanel(
      uiOutput("words_list"),
      hr(),
      uiOutput("dropdown_list")
    ), 
    mainPanel(
      h4("Results"),
      hr(),
      dataTableOutput("table")
    )
  )
)

# Create Server Function
server <- function(input, output) {
 
  # Output List of Dropdown Menus
  output$dropdown_list <- renderUI({
    lapply(words, function(x){
      selectInput(paste0("select_", x), x,
                  choices = choices)
    })
  })
  
  # Output Table of Results
  output$table <- renderDataTable({
    data.frame(word = words,
               type = sapply(words, function(x){
                 input[[paste0("select_", x)]]
               }))
  })

}

# Create Shiny App
shinyApp(ui = ui, server = server)

Your `input` is empty on start, so `input[[paste0('select_', x)]]` yields nothing, which is where the mismatch comes from. https://stackoverflow.com/questions/26147558/what-does-the-error-arguments-imply-differing-number-of-rows-x-y-mean — Anonymous coward, Dec 16 '22 at 21:32

score 1 · Accepted Answer · answered Dec 16 '22 at 21:33

When you use input widgets in renderUI(), the input$id will be NULL when the app starts until uiOutout("dropdown_list") is sent to the browser. Therefore, you need to verify that the inputs are not NULL when the table is rendered.

library(shiny)

words <- c("aapple", "apple", "bnanana", "pear", "banana")
# replace "" with " " 
choices = c(" ", "apple", "banana", "pear")

ui <- fluidPage(
  titlePanel("Matching Words with Dropdown Menus"),
  sidebarLayout(
    sidebarPanel(
      uiOutput("words_list"),
      hr(),
      uiOutput("dropdown_list")
    ), 
    mainPanel(
      h4("Results"),
      hr(),
      dataTableOutput("table")
    )
  )
)

server <- function(input, output) {
  output$dropdown_list <- renderUI({
    lapply(words, function(x){
      selectInput(paste0("select_", x), x,
                  choices = choices)
    })
  })
  
  output$table <- renderDataTable({
    data.frame(word = words,
               type = sapply(words, function(x){
                 # check with req()
                 req(input[[paste0("select_", x)]])
               }))
  })
  
}

shinyApp(ui = ui, server = server)

My general approach is to never use input widgets inside renderUI() because of this; and only using renderUI() for "outputs". With that paradigm, you would create the ui-Part of the app by using lapply() inside fluidPage(). You can then use updateSelectInput() if you want to change the choices over time.

Do you know why after this application is closed, the rest of my R code does not continue to execute? — megmac, Dec 20 '22 at 15:33

R Shiny Application Error String Matching

1 Answers1