Conditional cbind for dataframe in R Shiny

Question

I would like for the app user to select something from the drop-down list then enter a numeric value for it which would translate into a dataframe. If the same item is selected upon clicking the button n times, it would replace the original value, otherwise, it should cbind the new values into the dataframe. I don't know why there is a strange header on my dataframe as well. Please advise, thanks.

ui <- fluidPage(
    selectInput("solvent", "Choose a solvent:",
                list(`Solvent` = c("ETOH", "SALINE", "DW5",'CREMOPHOR','WATER','DMSO','2% KLUCEL (pH=4 /w HCl)')
    )),
    numericInput('vol','Vol solvent (ml)',0),
    actionButton('add','Add'),
    textOutput("result"),
    tableOutput('table')
)
  server = function(input, output) {

    rv <- reactiveValues()
      observeEvent(input$add,{rv$data<-data.frame(c(input$solvent,input$vol)); setNames(rv$data,input$solvent);
      if (as.numeric(input$add)>1 & colnames(rv$data) == input$solvent)
      {rv$data[1,input$solvent] = input$vol}
      else {cbind(rv$data,data.frame(input$solvent,input$vol))}
      })
    output$table<-renderTable({ rv$data})

    output$result <- renderText({
      paste("You chose", input$solvent)
    })
  }

shinyApp(ui, server)

Answer 1

Filling an empty dataframe and overwriting the values requires unfortunately a bit more than a two-liner. I suggest the following:

  rv <- reactiveValues()

  observeEvent(input$add, {
    if(is.null(rv$data)){
      rv$data <- data.frame(input$vol)
      names(rv$data) <- input$solvent
    } 
    rv$data[input$solvent] <- input$vol
  })

The full version you can find below:

ui <- fluidPage(
  selectInput("solvent", "Choose a solvent:",
              list(`Solvent` = c("ETOH", "SALINE", "DW5",'CREMOPHOR','WATER','DMSO','2% KLUCEL (pH=4 /w HCl)')
              )),
  numericInput('vol','Vol solvent (ml)',0),
  actionButton('add','Add'),
  textOutput("result"),
  tableOutput('table')
)
server = function(input, output) {

  rv <- reactiveValues()

  observeEvent(input$add, {
    if(is.null(rv$data)){
      rv$data <- data.frame(input$vol)
      names(rv$data) <- input$solvent
    } 
    rv$data[input$solvent] <- input$vol
  })

  output$table<-renderTable({ rv$data})

  output$result <- renderText({
    paste("You chose", input$solvent)
  })
}

shinyApp(ui, server)