Expand shinydashboard box to keep aspect ratio of facet_grid plot using shiny

Question

I have a select input that allows a user to select years to view a ggplot/facet grid plot. The plot will expand with each year. All that is fine but what I want is for the facetted plot to stay a consistent size regardless of how many years are selected and for the shinydashboard box to expand to keep the aspect ratio of each plot. Whether that means the box allows for scrolling or just adjust it's size. Either is fine! here is a simpler version of the code of what I had tried but isn't working. I also plan to have other boxes below the plot box that would need to adjust as needed as well.

library(shiny)
library(shinydashboard)
library(ggplot2)

# Function to generate ggplot with facet grid
generate_facet_plot <- function() {
  ggplot(mtcars, aes(x = mpg, y = hp)) +
    geom_point() +
    facet_wrap(~rownames(mtcars), scales = "free_y", ncol = 2) +
    theme(
      strip.text = element_text(size = 10),  # Set the minimum size for facet labels
      strip.background = element_rect(size = 20)  # Set the minimum size for facet background
    )
}

# Define UI
ui <- dashboardPage(
  dashboardHeader(title = "Facet Grid with Car Names"),
  dashboardSidebar(),
  dashboardBody(
    box(
      title = "Facet Grid Box",
      status = "primary",
      solidHeader = TRUE,
      width = 12,
      height = 500,  # Set a fixed height for the box
      div(style = "overflow-y: auto;",
          plotOutput("facet_plot")
      )
    )
  )
)

# Define server
server <- function(input, output) {
  output$facet_plot <- renderPlot({
    generate_facet_plot()
  })
}

# Run the application
shinyApp(ui, server)

Answer 1

Here is an approach building on a fixed box size and setting the plot height using the height= argument of renderPlot. In this case the user can scroll down or up if the plot does not fit into the size of the box. Tricky part is setting the plot height dynamically to ensure a constant aspect ratio or height of each facet panel. To this end I wrapped the renderPlot inside an observer (in general not recommended but I have not found a better option. Already tried a renderUI, but that breaks the scroll functionality and will result in the plot overflowing the boundaries of the box.). Inside the observer the plot height is set according to the num ber of rows of the facetted plot. Basically for a box with a height of 500px the maximum size for the plot is 400px. Hence, Additionally we have to account for the space occupied by the non data ink, e.g. the font size of the axis title and text, ... .

Note: If you want to adjust the size of the box instead, it's in principle the same approach. But in this case we have to set the box height.

library(shiny)
library(shinydashboard)
library(ggplot2)

mtcars2 <- mtcars
mtcars2$model <- rownames(mtcars)

# Function to generate ggplot with facet grid
generate_facet_plot <- function(.data) {
  ggplot(.data, aes(x = mpg, y = hp)) +
    geom_point() +
    facet_wrap(~model, scales = "free_y", ncol = 2) +
    theme(
      strip.text = element_text(size = 10), # Set the minimum size for facet labels
      strip.background = element_rect(size = 20) # Set the minimum size for facet background
    )
}

# Define UI
ui <- dashboardPage(
  dashboardHeader(title = "Facet Grid with Car Names"),
  dashboardSidebar(
    selectInput(
      "model",
      "Select models",
      choices = rownames(mtcars),
      selected = rownames(mtcars),
      multiple = TRUE
    )
  ),
  dashboardBody(
    box(
      title = "Facet Grid Box",
      status = "primary",
      solidHeader = TRUE,
      width = 12,
      height = 500, # Set a fixed height for the box
      div(
        style = "overflow-y: auto;",
        plotOutput("facet_plot")
      )
    )
  )
)

# Define server
server <- function(input, output) {
  mtcars_filtered <- reactive({
    mtcars2 |>
      subset(model %in% input$model)
  })

  observe({
    req(input$model)
    # Set for your theme
    base_size <- 11
    plot_margin <- 2 * 5.5
    axis_title <- base_size
    axis_text <- .8 * base_size
    axis_text_margin <- 2.2
    axis_ticks_length <- 2.75
    # Non data ink
    height_non_data_ink <- plot_margin + 
      axis_title + axis_text + axis_text_margin + axis_ticks_length
    # Half of max content height in box
    row_height <- (400 - height_non_data_ink) / 2
    nrow <- (length(input$model) - 1) %/% 2 + 1
    height <- nrow * row_height + height_non_data_ink
    output$facet_plot <- renderPlot(
      {
        generate_facet_plot(mtcars_filtered())
      },
      height = height
    )
  })
}

# Run the application
shinyApp(ui, server)