add shiny example of dragging lines

Author: cpsievert

inst/examples/shiny/drag_lines/app.R

@@ -0,0 +1,46 @@
+library(shiny)
+library(plotly)
+
+ui <- fluidPage(
+  plotlyOutput("p"),
+  verbatimTextOutput("event")
+)
+
+x <- seq(-10, 10)
+y <- rnorm(length(x))
+
+
+server <- function(input, output, session) {
+  
+  output$p <- renderPlotly({
+    
+    d <- event_data("plotly_relayout", source = "trajectory")
+    
+    selected_point <- if (!is.null(d[["shapes[0].x0"]])) {
+      xint <- d[["shapes[0].x0"]]
+      xpt <- x[which.min(abs(x - xint))]
+      list(x = xpt, y = y[which(x == xpt)])
+    } else {
+      list(x = 1, y = y[which(x == 1)])
+    }
+    
+    plot_ly(color = I("red"), source = "trajectory") %>%
+      add_lines(x = x, y = y) %>%
+      add_markers(x = selected_point$x, y = selected_point$y) %>%
+      layout(
+        shapes = list(
+          type = "line", 
+          line = list(color = "gray", dash = "dot"),
+          x0 = selected_point$x, 
+          x1 = selected_point$x,
+          y0 = 0,
+          y1 = 1,
+          yref = "paper"
+        )
+      ) %>%
+      config(editable = TRUE)
+  })
+  
+}
+
+shinyApp(ui, server)