add shiny streaming example; improve a couple others

Author: cpsievert

inst/examples/shiny/stream/app.R

@@ -0,0 +1,60 @@
+library(shiny)
+library(plotly)
+
+ui <- fluidPage(
+  actionButton("stream", "Turn stream on/off"),
+  plotlyOutput("plot")
+)
+
+server <- function(input, output, session) {
+  
+  # initial values
+  yint <- c(0, 1)
+  
+  # initiate graph with initial values
+  output$plot <- renderPlotly({
+    plot_ly(y = yint, x = seq_along(yint)) %>%
+      add_lines()
+  })
+  
+  # reactiveValues() act very much like input values, but may be used to 
+  # maintain state (e.g., are we currently streaming?)
+  rv <- reactiveValues(
+    stream = FALSE,
+    yend = sum(yint), 
+    n = length(yint)
+  )
+  
+  # turn streaming on/off when the button is pressed
+  observeEvent(input$stream, {
+    rv$stream <- if (rv$stream) FALSE else TRUE
+  })
+  
+  observe({
+    # if we're not streaming, don't do anything
+    if (!rv$stream) return()
+    
+    # re-execute this code block to every 100 milliseconds
+    invalidateLater(100, session)
+    # changing a reactive value "invalidates" it, so isolate() is needed 
+    # to avoid recursion
+    isolate({
+      rv$n <- rv$n + 1
+      rv$yend <- rv$yend + sample(c(-1, 1), 1)
+    })
+    
+    # add the new value to the plot
+    plotlyProxy("plot", session) %>%
+      plotlyProxyInvoke(
+        "extendTraces", 
+        list(
+          y = list(list(rv$yend)), 
+          x = list(list(rv$n))
+        ), 
+        list(0)
+      )
+  })
+  
+}
+
+shinyApp(ui, server)