Thanks Mara, sorry to be stupid but because I'm doing a scatter plot I can only feed in a data frame with 2 vars.
As I'm doing it on a Shiny app I'm also using reactive to refresh the data frame (I've copied the relevant bits of code below).
I've tried a few different approaches from your link but can't get it working...
graph_data <- reactive({epl_in[, c(input$xvar, input$yvar)]})
output$plot <- renderGvis({
gvisScatterChart(graph_data(),
options=list(legend = "none",
title = paste('Scatter plot of ',input$xvar, ' by ',input$yvar),
vAxis = paste("{title: '", input$yvar, "'}"),
hAxis = paste("{title: '", input$xvar, "'}"),
width = 800,
height = 600))
})