R / R Shiny - global dataframes array (assigned by reference)? - r

Question

I have a dataframe df1, and subset it to df1sub and display it in an R shiny renderPlot() call. Similarly, I have df2, and I subset it to df2sub, and render it in R shiny via a separate renderPlot() call. Btw these subsets are created based on user choices in an R Shiny app.
Now, I have a datatable that I want to change to reflect whatever the current dataset is, so I wanted some kind of global like:
buffers[1] <- df1sub
buffers[2] <- df2sub
How would I go about defining this global var? I tried separately doing buffers = array() to initialize a global var but then the assignments as I wrote them above don't work?
Update: attempts to use the the '<<-' operator as suggested below yields the following:
buffers <- NULL #don't know how else to initialize. array() yields same error as below.
buffers[1] <<- df # Error in buffers[1] <<- df : object 'buffers' not found

Answer 1

You can adopt this approach:
library(shiny)
shinyServer(function(input, output) {
...
some.reactive.expression <- reactive1({
...
buffers[1] <<- df1sub
buffers[2] <<- df2sub
...
})
})
With some updates:
#In global.R
buffers <- list()
buffers[[1]] <- data.frame()
buffers[[2]] <- data.frame()
buffers[[1]] <- df1 #original dataset, as a default, before subsets are created
buffers[[2]] <- df2 #ditto.
Then in server.R:
r1 <- reactive({
... #create subset of df, then return it
buffers[[1]] <<- subset(...)
buffers[[1]] #return it as dynamic data for plots
})
r2 <- reactive({...}) #ditto
then in renderplot:
output$blah <- renderplot(r1()...)
output$foo <- renderplot(r2()...)
Leaving the global buffers[] var separately available to a 3rd UI widget (e.g. a data table)...