Unexpected values from text input in Rshiny - r

Question

I am making an app that takes input from a slider to create the matching number of input text boxes. However, when I print the values from the input boxes it does not always update.
Example:
Pick 3 on slider input. Put 1,2,3 into the 3 text boxes respectively.Hit submit. Prints number = 1 number = 2 number = 3. When I move the slider to 2 and hit enter, I get number = 1 number = 2 despite no values being in the text input anymore. If I move the slider to 4, I will than get the output number = NA number = NA number = 3 number = NA.
Clearly it is remembering previous input values, but I cannot understand why or how to fix it.
ui.R
shinyUI(fluidPage(
fluidRow(
column(4, wellPanel(
sliderInput("numObs", "Number of observations", 1, 30, 3),
uiOutput("buttons"),
submitButton(text = "Apply Changes", icon = NULL)
)),
column(8,
textOutput("a")
)
)
))
server.R
shinyServer(function(input, output) {
output$buttons <- renderUI({
obs <- input$"numObs";
objs <-list();
for (i in 1:obs ){
objs <- list(objs, numericInput(inputId = paste0("t", i), "Day:", NA),br());
}
objs <- fluidRow(objs);
})
t<- function(){
for(i in 1:input$"numObs"){
if(i ==1){
t <- c(as.numeric(input[[paste0("t",i)]])[1]);
}
else{
t <- c(t,as.numeric(input[[paste0("t",i)]])[1]);
}
}
return(t);
}
output$a<- renderText({
paste("number = ", t());
})
})

Answer 1

I made some changes and introduced a few things to your code. Its better to use actionButton than the submitButton as it is more flexible. If you dont like the style of the actionButton, look into Shiny Themes
rm(list = ls())
library(shiny)
ui =(fluidPage(
fluidRow(
column(4, wellPanel(
sliderInput("numObs", "Number of observations", 1, 30, 3),
uiOutput("buttons"),
actionButton("goButton", "Apply Changes")
)),
column(8,textOutput("a"))
) ))
server = (function(input, output) {
output$buttons <- renderUI({
obs <- input$"numObs";
objs <-list();
for (i in 1:obs ){
objs <- list(objs, numericInput(inputId = paste0("t", i), "Day:", NA),br());
}
objs <- fluidRow(objs);
})
# keep track if the Number of obseervations change
previous <- eventReactive(input$goButton, {
input$numObs
})
t <- eventReactive(input$goButton, {
for(i in 1:input$"numObs"){
if(i ==1){
t <- c(as.numeric(input[[paste0("t",i)]])[1]);
}
else{
t <- c(t,as.numeric(input[[paste0("t",i)]])[1]);
}
}
return(t)
})
output$a<- renderText({
if(previous() != input$numObs){
return()
}
paste("number = ", t());
})
})
runApp(list(ui = ui, server = server))