I'm running into the error "Error in <-: invalid (NULL) left side of assignment" over and over again as I attempt to take a reactive object in Shiny and further manipulate it. I've provided an illustrative example below.

```
 testdf <- data.frame(row1 = c(1,3,6), row2 = c(7, 5, 1))

 ui <- fluidPage(

   titlePanel("Education in Tanzania"),

   sidebarLayout(
     sidebarPanel(

       #Select aggregation level of data
       selectInput("AggregationSelect", 
                   label = "Aggregation",
                   choices = list("School" = 1, 
                                  "District" = 2, 
                                  "Region" = 3),
                   selected = 1)
     ),

     mainPanel(
       DT::dataTableOutput("OutputTable")
     )
   )
 )

 server <- function(input, output) {

     Output1 <- reactive({
         testdf
     })

   observe({
     if(2 %in% input$AggregationSelect) {
       observe({Output1()$name[3] <- "b"})
     } else  if(3 %in% input$AggregationSelect) {
       observe({Output1()$name[2] <- "c"})
     } else  if(1 %in% input$AggregationSelect) {
       observe({Output1()$name[1] <- "a"})
     }
   })

   output$OutputTable <- {DT::renderDataTable({
     DT::datatable(Output1(),
                   options = list(pagelength = 25,
                                  searching = TRUE,
                                  paging = TRUE,
                                  lengthChange = FALSE),
                   rownames = FALSE)
     })
   }
 }  

 shinyApp(ui = ui, server = server)

```

What I need to do in my actual code is assemble a dataframe through the UI (which I am able to do and therefore have just subbed a random df in here) and then add some information (represented here with the added "names" column) based on what has been selected in the UI. It seems like it shouldn't be all that difficult to add a column to a df, but within the reactive object context, nothing I have attempted has worked. Other ways to modify reactive objects are welcome as long as they can be applied to more complex multi-step scenarios - there's no way I can get everything I need bundled into the initial assignment of the reactive object.