renderPlot priority (and/or nesting reactivity)

[Jonathan]

Hi,

I have 3 plots that depend on the same data. For example, something like this:

get_data <- reactive({ <read .csv file> })

output$p1 <- renderPlot({plot(get_data()$x,get_data()$y1)})

output$p2 <- renderPlot({plot(get_data()$x,get_data()$y2)})

output$p3 <- renderPlot({plot(get_data()$x,get_data()$y3)})

I would like guarantee they update in a specified order. It seems like I could do this one of two ways that both require nesting reactivity. 1) using 'priority' option of multiple observe's or 2) nesting the renderPlots in one observe. But I don't know if/when/how nesting reactivity like this is ok, or if it behaves like I think. I haven't found a good article that talks about it. 

What happens when we put a 'renderPlot' inside an 'observe'? Is either of these kosher and/or is there a better way?

1) using 'priority':

get_data <- reactive({ <read .csv file> })

observe({output$p1 <- renderPlot({plot(get_data()$x,get_data()$y1)}),priority=3)}

observe({output$p2 <- renderPlot({plot(get_data()$x,get_data()$y2)}),priority=2)}

observe({output$p3 <- renderPlot({plot(get_data()$x,get_data()$y3)}),priority=1)}

2) nesting renderPlot in one observe:

get_data <- reactive({ <read .csv file> })

observe({

  output$p1 <- renderPlot({plot(get_data()$x,get_data()$y1)})

  output$p2 <- renderPlot({plot(get_data()$x,get_data()$y2)})

  output$p3 <- renderPlot({plot(get_data()$x,get_data()$y3)})

})

Jonathan

[Joe Cheng]

No, neither option will work. `output$p1 <- renderPlot(...)` doesn't mean "Update p1 right now with this renderPlot data", instead it means "p1 should always be filled with the up-to-date result of this expression". In other words, there's already an observer being created when you assign something to output$whatever, and creating an observer from inside an observer is a Bad Smell--its behavior is well-defined but almost always a sign that you're going about the problem the wrong way.

Instead, do this:

outputOptions(output, "p1", priority = 3)

outputOptions(output, "p2", priority = 2)

outputOptions(output, "p3", priority = 1)

This will ensure that the priority is set on the observers that underlie those outputs.

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