how to display elements of a character vector one by one

Question

I have a character vector corpus . I am trying to display each member of the vector one by one as I click the Next button. How can I increment the current variable using Next button?
So far I have the following code:

#ui.R
library(shiny)
shinyUI(fluidPage(
  titlePanel("Display character vector one by one"),
  sidebarLayout(sidebarPanel(actionButton("Next", "Next Sentence")),
  mainPanel( htmlOutput("content"))
)))

#server.R
shinyServer(function(input, output) {
  corpus <- c("Sample sentence one", "Second sentence", "Third sentence")
  current <- 1 
  observeEvent(input$Next,{
    if(current <= length(corpus))
    output$content <- renderText(corpus[current])
  })
})

Please also suggest if there are better ways to achieve this functionality

Answer 1

The problem is:

In your server.R , you make the variable current local, so every time you click the button Next Sentence , it remains constantly 1 , as a result, it will always render the first element in your list, which is Sample sentence one .

Solution:

Make a global variable, increase by 1 after every time you click the button. In RShiny , use <<- to modify global variable instead of <- . Also check Scoping rules for Shiny apps .

So check:

current <- 0

shinyServer(function(input, output) {
  corpus <- c("Sample sentence one", "Second sentence", "Third sentence")
  observeEvent(input$Next,{
    if(current <= length(corpus))
      output$content <- renderText(corpus[current])

    current <<- current %% length(corpus) + 1
  })
})

Answer 2

You can try this too, store the current index as reactive value and show the sentences circularly, with modulo arithmetic:

#ui.R
library(shiny)
ui <- shinyUI(fluidPage(
  titlePanel("Display character vector one by one"),
  sidebarLayout(sidebarPanel(actionButton("Next", "Next Sentence")),
                mainPanel( htmlOutput("content"))
  )))

#server.R
server <- shinyServer(function(input, output) {
  values <- reactiveValues()
  values$current <- 0
  corpus <- c("Sample sentence one", "Second sentence", "Third sentence")
  observeEvent(input$Next,{
    output$content <- renderText(corpus[values$current])
    values$current <- values$current %% length(corpus) + 1
  })
})
shinyApp(ui = ui, server = server)