Using reactive variable to change a subset of data using Shiny

Question

I have a data set spanning several years. My shiny app is intended to let the user step through one week at a time, do some analysis and update the data set with new information for that week. e.g. the schedule.

In normal R, I do the following code, where update_schedule is a custom function:

data[indx:(indx+7)] <- update_data(data[indx:(indx+7)], schedule)

Using shiny, I am trying to do something similar, but getting the error:

Error in .getReactiveEnvironment()$currentContext() : Operation not allowed without an active reactive context. (You tried to do something that can only be done from inside a reactive expression or observer.)

#ui
shinyUI(pageWithSidebar(
  sidebarPanel(
  actionButton("nextButton", "Process Next Week")
  ),

  mainPanel(
    textOutput('week'),
    plotOutput('myplot')
  )
))


#server
data <<- data.frame(value = rep(1:4, 3:6), open = rep(c(1,1,0), 6))

shinyServer(function(input, output) ({

  week <- reactive({as.numeric(input$nextButton)+1})
  output$week <- renderText({week()})

  #this is the problem line
  data[(week()*7):((week()+1)*7)]$open <<- rep(1,7)

  #but here the sub-setting works for plotting
  output$myplot <- renderPlot({
      p1 <- plot(data$value[(week()*7):((week()+1)*7)], 
       col = as.factor(data$open)[(week()*7):((week()+1)*7)])
      return(p1)
     })

  })
)

Is there a way to use the week() value to select a portion of data to update? Also, in reality I am trying to update several variables at once, not just the "open" column in this example.

I tried the following to keep my reactive variables in a reactive statement, but got an error:

data <<- reactive({data %>%
  mutate(open = replace(open, (week()*7):((week()+1)*7, rep(1,7))})

Error in plot(data()$value[(week() * 7):((week() + 1) * 7)], col = as.factor(data()$open)[(week() *  : 
error in evaluating the argument 'x' in selecting a method for function 'plot': Error in UseMethod("mutate_") : 
no applicable method for 'mutate_' applied to an object of class "reactive"

Answer 1

Did you read and fully understand the reactive expressions chapter of the shiny tutorial? http://shiny.rstudio.com/tutorial/lesson6/

Any expression that uses a reactive expression (week is reactive since you define it with a reactive({}) must be used inside a reactive context, such as another reactive() call or inside observe or renderXXX. You should also look at reactiveValues() function