Creating Tooltips Next to Axis Titles in Plotly

In data visualization, adding meaningful and interactive annotations to plots is crucial for understanding complex data. In R Shiny applications, particularly those built with the plotly package, creating tooltips next to axis titles can enhance user engagement and insight. This guide explores how to achieve this functionality using HTML, CSS, JavaScript, and plotly.

Understanding the Problem

When working with plots in R Shiny, especially those generated by plotly, it’s common to need additional information about the data being visualized. While default annotations like axis titles provide a good starting point, they can sometimes lack context or clarity. By adding tooltips next to these titles, users can quickly access more detailed explanations of what each axis represents.

The Challenge

One major challenge in achieving this functionality is that plotly doesn’t have a built-in way to add tooltips directly to axis titles. However, by leveraging HTML and CSS techniques combined with JavaScript, we can create custom containers around the axis titles to serve as tooltips.

Leveraging Plotly’s Customization Capabilities

Plotly allows for extensive customization through its API. By utilizing HTML widgets and onRender events, we can dynamically update elements of our plot to accommodate tooltips. In this solution, we’ll define a container element in CSS that will be used to hold the tooltip content.

The Solution

The following code snippet demonstrates how to create a Shiny application with plotly that includes axis title tooltips:

library(shiny)
library(plotly)

ui <- fluidPage(
  tags$head(
    tags$script(jscode),
    tags$style(csscode)
  ),
  div(class = "plot-container",
      plotlyOutput("plot"),
      div(
        class = "xaxis-container",
        div(class = "xaxis-tooltip", "data-toggle" = "tooltip", "title" = "X Axis")
      ),
      div(
        class = "yaxis-container",
        div(class = "yaxis-tooltip", "data-toggle" = "tooltip", "title" = "Y Axis")
      )
  )
)

server <- function(input, output) {
  output$plot <- renderPlotly({
    plot_ly() %>% 
      add_trace(
        data = data.frame(a = c(1, 2, 3), b = c(4, 5, 6)),
        x = ~a,
        y = ~b,
        type = "scatter"
      ) %>% 
      htmlwidgets::onRender("
        function(el, x) {
          var width = $('.draglayer')[0].getBoundingClientRect().width;
          var height = 0.5*$('.yaxis-tooltip')[0].getBoundingClientRect().height+$('.plot-container')[0].getBoundingClientRect().height-0.5*$('.draglayer')[0].getBoundingClientRect().height;
          $('.xaxis-container').css('width', width);
          $('.yaxis-container').css('height', height);
        }
      ")
  })
}

shinyApp(ui, server)

Explanation

This solution involves the following components:

1. HTML: We define two div elements within our plot container (xaxis-container and yaxis-container). Each of these containers will serve as a tooltip holder for its respective axis title.
2. CSS: In the CSS code block, we create styles to position the tooltip holders absolutely at the bottom left of their parent elements. The width attribute is dynamically set based on the content’s width ($('.draglayer')[0].getBoundingClientRect().width) and the height attribute is calculated similarly but with adjustments for the plot container height.
3. JavaScript: Within the JavaScript code block, we initialize a tooltip plugin to append the tooltip holder element (<div class='xaxis-tooltip'>) to the page body when initialized.

Example Use Case

By implementing this solution in your R Shiny application, you can enhance user interaction and clarity by providing tooltips next to axis titles. This makes it easier for users to quickly understand the meaning behind each axis on a plot.

Best Practices

• Always use meaningful and descriptive variable names throughout your code.
• Consider including comments or documentation to explain any complex logic or customizations in your solution.
• Test thoroughly to ensure that all components of your solution work as expected.

Last modified on 2023-06-20