Answer by HubertL for How to get data out of reactive function in Shiny to create new columns on the same DF

You have to put the reactive out of the function, for example you can call the function from the reactive:

shinyServer(function(input, output, session)  {  generate <- function(dates){    listofdfs <- list() #Create a list in which you intend to save your df's.     for (i in 1:length(dates)){      data <- dbGetQuery(con, sprintf("select Column A, CAST (date AS date), id from My_Table                                                 where id =", input$user_id," and                                                date <= '%s' and date >= '%s'- INTERVAL '7 days'", dates[i], dates[i]))      data$Column_A_mean <- mean(data[,1]) #creating a new column like we do in a data frame (DF)      listofdfs[[i]] <- data() # save your dataframes into the list    }    return(listofdfs) #Return the list of dataframes.  }  df <- reactive({do.call("rbind", generate(dates))})  output$Coolplot <- renderPlot({    ggplot(data = df(), aes(date)) +      geom_line(aes(y = Column A, colour = "Column A"))+      geom_line(aes(y = Column_A_mean, colour = "Column_A_mean"))  })})