# Usage with shiny

# TL;DR

See a working application here

# More detail

The equatiomatic package exports `renderEq()` and `eqOutput()` functions to make it’s usage with shiny more straightforward.

Imagine, for example, that we wanted to have an app that showed us the coefficients of a model in a nice table. We could do that with something like

    library(equatiomatic)
    library(shiny)
    library(shinyWidgets)
    library(gtsummary)
    library(gt)

    data("penguins", package = "equatiomatic")

    ui <- fluidPage(
      titlePanel("equatiomatic w/Shiny"),
      sidebarLayout(
        sidebarPanel(
          multiInput(
            inputId = "xvars", label = "Select predictor variables :",
            choices = names(penguins)[-3],
            selected = "island"
          )
        ),
        mainPanel(
          gt_output("tbl")
        )
      )
    )

    server <- function(input, output) {
      model <- reactive({
        form <- paste("bill_length_mm ~ ", paste(input$xvars, collapse = " + "))
        lm(as.formula(form), penguins)
      })

      output$tbl <- render_gt({
        as_gt(tbl_regression(model()))
      })

    }

    shinyApp(ui = ui, server = server)

But, naturally, we’d probably also want the equation rendered too. We can extend The above with equatiomatic as follows.

    library(equatiomatic)
    library(shiny)
    library(shinyWidgets)
    library(gtsummary)
    library(gt)

    ui <- fluidPage(
      titlePanel("equatiomatic w/Shiny"),
      withMathJax(), # Initialize mathJax so the equation renders properly
      sidebarLayout(
        sidebarPanel(
          multiInput(
            inputId = "xvars", label = "Select predictor variables :",
            choices = names(penguins)[-3],
            selected = "island"
          )
        ),
        mainPanel(
          eqOutput("equation"),
          gt_output("tbl")
        )
      )
    )

    server <- function(input, output) {
      model <- reactive({
        form <- paste("bill_length_mm ~ ", paste(input$xvars, collapse = " + "))
        lm(as.formula(form), penguins)
      })

      output$equation <- renderEq(
        extract_eq(model())
      )

      output$tbl <- render_gt({
        as_gt(tbl_regression(model()))
      })

    }

    shinyApp(ui = ui, server = server)

Note that, beyond the `renderEq()` and `eqOutput()` function, we also have to initialize mathJax with the `shiny::withMathJax()` function somewhere in the UI. Without this line, you’ll get the text version of the equation.

Finally, we can of course add additional arguments `extract_eq()`, and it all works as expected.

    library(equatiomatic)
    library(shiny)
    library(shinyWidgets)
    library(gtsummary)
    library(gt)

    ui <- fluidPage(
      titlePanel("equatiomatic w/Shiny"),
      withMathJax(),
      sidebarLayout(
        sidebarPanel(
          multiInput(
            inputId = "xvars",
            label = "Select predictor variables :",
            choices = names(penguins)[-3],
            selected = "island"
          )
        ),
        mainPanel(
          eqOutput("eq2"),
          eqOutput("equation"),
          gt_output("tbl")
        )
      )
    )

    server <- function(input, output) {
      model <- reactive({
        form <- paste("bill_length_mm ~ ", paste(input$xvars, collapse = " + "))
        lm(as.formula(form), penguins)
      })

      output$equation <- renderEq(
          extract_eq(
            model(),
            wrap = TRUE,
            terms_per_line = 2,
            use_coefs = TRUE,
            font_size = "Huge"
        )
      )

      output$tbl <- render_gt({
        as_gt(tbl_regression(model()))
      })

    }

    shinyApp(ui = ui, server = server)