Creating a new column for a reactive data block in shiny / shiny panel R

Question

inside the server for my shinyApp, I created a data frame based on inputs. However, I want to add a new column that uses two columns of this frame.

server <- function(input, output, session) {
  l.out <- reactive({
    BatchGetSymbols(tickers = input$stock, 
                first.date = Sys.Date() - as.integer(input$length),
                last.date = Sys.Date())
  })
  stock_info <- reactive({
    l.out()$df.tickers
  })
  stock_info()$return <- reactive({
    rep(0, length(stock_info()$ref.date))
  })
  stock_info()$return <- reactive({
    for (i in 2:length(stock_info()$ref.date)){
      stock_info()$return[i] <- ((stock_info()$price.close[i] - 
stock_info()$price.close[i - 1]) / stock_info$price.close[i - 1])
    }
  })

I tried it like this and it works until I try to create share_info () $ return, where I always get an error that NULL leaves. Any tips?

Answer 1

I am not familiar with the package BatchGetSymbols, but the concepts in the example below should be applicable to your use case.

First of all, due to the lack of an elegant way of saying this, I am sure that the expression ...

  stock_info()$return <- reactive({
    rep(0, length(stock_info()$ref.date))
  })

... , shiny .

, , . , , .

library(shiny)

ui <- fluidPage(
  textInput('stock','stock',"GE"),
  sliderInput('length', 'length', min = 1, max = 10, value = 5),
  dataTableOutput('my_table')
)

server <- function(input, output, session) {

  ## This will update whenever either input$length or input$stock change
  stock_info <- reactive({

    length <- as.integer(input$length)

    temp_stock_info <- data.frame(stock = input$stock,
                                  foo = seq_len(length),
                                  bar = rnorm(length))

    temp_stock_info$baz <- paste("xxx",length)

    return(temp_stock_info)
  })

  ## Return an output
  output$my_table <- renderDataTable({
    stock_info()
  })
}

shinyApp(ui, server)

, l.out , . l.out , , .

, , stock_info, , l.out l.out .

library(shiny)

ui <- fluidPage(
  textInput('stock','stock',"GE"),
  sliderInput('length', 'length', min = 1, max = 100, value = 50),
  sliderInput('displayLength', 'displayLength', min = 1, max = 20, value = 5),
  dataTableOutput('my_table')
)

server <- function(input, output, session) {

  ## l.out will change with input$length and input$stock
  ## but NOT input$displayLength
  l.out <- reactive({
    data.frame(stock = input$stock,
               foo = rnorm(input$length),
               l.out_update_time = Sys.time())
  })

  ## stock_info will update whenever l.out changes or the displayLength changes. 
  ## l.out will NOT be updated if only input$displayLength changes
  stock_info <- reactive({
    tmp_stock_info <- head(x = l.out(), n = input$displayLength)
    tmp_stock_info$stock_info_update_time <- Sys.time()
    return(tmp_stock_info)
  })

  ## Return an output
  output$my_table <- renderDataTable({
    stock_info()
  })
}

shinyApp(ui, server)