## Dynamically add panel

You can add panels to an existing dock with `add_panel()` which expects a `panel()` object.

Toggle code

    library(dockViewR)
    library(shiny)
    library(bslib)
    library(visNetwork)

    options("dockViewR.mode" = "dev")

    nodes <- data.frame(id = 1:3)
    edges <- data.frame(from = c(1, 2), to = c(1, 3))

    ui <- page_fillable(
      actionButton("btn", "add Panel"),
      dockViewOutput("dock")
    )

    server <- function(input, output, session) {
      dock_proxy <- dock_view_proxy("dock")

      exportTestValues(
        panel_ids = get_panels_ids(dock_proxy),
        active_group = get_active_group(dock_proxy),
        grid = get_grid(dock_proxy)
      )

      output$dock <- renderDockView({
        dock_view(
          add_tab = new_add_tab_plugin(enable = TRUE),
          panels = list(
            panel(
              id = "1",
              title = "Panel 1",
              content = tagList(
                sliderInput(
                  "obs",
                  "Number of observations:",
                  min = 0,
                  max = 1000,
                  value = 500
                ),
                plotOutput("distPlot")
              )
            ),
            panel(
              id = "2",
              title = "Panel 2",
              content = tagList(
                visNetworkOutput("network")
              ),
              position = list(
                referencePanel = "1",
                direction = "right"
              ),
              minimumWidth = 500
            ),
            panel(
              id = "3",
              title = "Panel 3",
              content = tagList(
                selectInput(
                  "variable",
                  "Variable:",
                  c("Cylinders" = "cyl", "Transmission" = "am", "Gears" = "gear")
                ),
                tableOutput("data")
              ),
              position = list(
                referencePanel = "2",
                direction = "below"
              )
            )
          ),
          theme = "replit"
        )
      })

      output$distPlot <- renderPlot({
        req(input$obs)
        hist(rnorm(input$obs))
      })

      output$network <- renderVisNetwork({
        visNetwork(nodes, edges, width = "100%")
      })

      output$data <- renderTable(
        {
          mtcars[, c("mpg", input$variable), drop = FALSE]
        },
        rownames = TRUE
      )

      output$plot <- renderPlot({
        dist <- switch(
          input$dist,
          norm = rnorm,
          unif = runif,
          lnorm = rlnorm,
          exp = rexp,
          rnorm
        )

        hist(dist(500))
      })

      observeEvent(input$btn, {
        pnl <- panel(
          id = "new_1",
          title = "Dynamic panel",
          content = tagList(
            radioButtons(
              "dist",
              "Distribution type:",
              c(
                "Normal" = "norm",
                "Uniform" = "unif",
                "Log-normal" = "lnorm",
                "Exponential" = "exp"
              )
            ),
            plotOutput("plot")
          ),
          position = list(
            referencePanel = "1",
            direction = "within"
          ),
          remove = new_remove_tab_plugin(enable = TRUE, mode = "manual")
        )
        add_panel(
          dock_proxy,
          pnl
        )
      })

      observeEvent(input[["dock_added-panel"]], {
        showNotification(
          paste("Panel added:", input[["dock_added-panel"]]),
          type = "message"
        )
      })

      # Manually remove a panel after clicking on the button
      observeEvent(input[["dock_panel-to-remove"]], {
        showNotification(
          paste("Removing panel:", input[["dock_panel-to-remove"]]),
          type = "message"
        )
        remove_panel(
          dock_proxy,
          input[["dock_panel-to-remove"]]
        )
      })

      # Manually add a panel after clicking on the + button
      observeEvent(input[["dock_panel-to-add"]], {
        add_panel(
          dock_proxy,
          panel(
            id = as.character(as.numeric(tail(get_panels_ids(dock_proxy), 1)) + 1),
            title = paste(
              "Panel",
              as.character(as.numeric(tail(get_panels_ids(dock_proxy), 1)) + 1)
            ),
            content = paste(
              "This is panel",
              as.character(as.numeric(tail(get_panels_ids(dock_proxy), 1)) + 1)
            ),
            position = list(
              referenceGroup = input[["dock_panel-to-add"]],
              direction = "within"
            )
          )
        )
      })
    }

    shinyApp(ui, server)

An alternative way to add panels is to use the `+` icon next to the panel tabs. For this, you make sure to initialize the dock with `add_tab = list(enable = TRUE)`. By default, a callback function sets a Shiny input value `input$<dock_id>_panel-to-add` to the id of group where the panel should belong. You can listen to this input on the server side to manually call `add_panel()`. Make sure that the panel is passed like so:

    add_panel(
      dock_id,
      panel = panel(
        id = "new_id",
        position = list(
          referenceGroup = input[["<dock_id>_panel-to-add"]],
          direction = "right"
        )
      )
    )

To add a floating panel, you can set `floating = TRUE` when calling `add_panel()`.

## Dynamically remove panels

You can remove panels from an existing dock with `remove_panel()` which expects the `id` of the panel to remove, in addition to the dock `id`.

Toggle code

    library(dockViewR)
    library(shiny)
    library(bslib)
    library(visNetwork)

    options("dockViewR.mode" = "dev")

    nodes <- data.frame(id = 1:3)
    edges <- data.frame(from = c(1, 2), to = c(1, 3))

    ui <- page_fillable(
      selectInput("selinp", "Panel ids", choices = NULL),
      actionButton("btn", "remove Panel"),
      dockViewOutput("dock")
    )

    server <- function(input, output, session) {
      dock_proxy <- dock_view_proxy("dock")

      exportTestValues(
        panel_ids = get_panels_ids(dock_proxy),
        active_group = get_active_group(dock_proxy),
        grid = get_grid(dock_proxy)
      )
      observeEvent(get_panels_ids(dock_proxy), {
        updateSelectInput(
          session = session,
          inputId = "selinp",
          choices = get_panels_ids(dock_proxy)
        )
      })

      output$dock <- renderDockView({
        dock_view(
          panels = list(
            panel(
              id = "1",
              title = "Panel 1",
              content = tagList(
                sliderInput(
                  "obs",
                  "Number of observations:",
                  min = 0,
                  max = 1000,
                  value = 500
                ),
                plotOutput("distPlot")
              )
            ),
            panel(
              id = "2",
              title = "Panel 2",
              content = tagList(
                visNetworkOutput("network")
              ),
              position = list(
                referencePanel = "1",
                direction = "right"
              ),
              minimumWidth = 500
            ),
            panel(
              id = "3",
              title = "Panel 3",
              content = tagList(
                selectInput(
                  "variable",
                  "Variable:",
                  c("Cylinders" = "cyl", "Transmission" = "am", "Gears" = "gear")
                ),
                tableOutput("data")
              ),
              position = list(
                referencePanel = "2",
                direction = "below"
              )
            )
          ),
          theme = "replit"
        )
      })

      output$distPlot <- renderPlot({
        req(input$obs)
        hist(rnorm(input$obs))
      })

      output$network <- renderVisNetwork({
        visNetwork(nodes, edges, width = "100%")
      })

      output$data <- renderTable(
        {
          mtcars[, c("mpg", input$variable), drop = FALSE]
        },
        rownames = TRUE
      )

      output$plot <- renderPlot({
        dist <- switch(
          input$dist,
          norm = rnorm,
          unif = runif,
          lnorm = rlnorm,
          exp = rexp,
          rnorm
        )

        hist(dist(500))
      })

      observeEvent(input$btn, {
        req(input$selinp)
        remove_panel(dock_proxy, input$selinp)
      })
    }

    shinyApp(ui, server)

## Dynamically move panel

You can move individual panels in the dock with `move_panel()` which expects:

- The dock id.
- The panel id: can be a string or numeric value.
- The position. If left NULL, the panel is moved to the latest index. Otherwise choose one of `"left", "right", "top", "bottom", "center"`.
- `group`: id of the panel that belongs to another group. The panel will be moved relative to the second group, depending on the position parameter. If left NULL, it is added on the right side.
- index: If panels belong to the same group, you can use index to move the target panel at the desired position. When group is left NULL, index must be passed and cannot exceed the total number of panels or be negative.

Toggle code

    library(shiny)
    library(bslib)
    library(dockViewR)

    options("dockViewR.mode" = "dev")

    ui <- fluidPage(
      h1("Panels within the same group"),
      actionButton("move", "Move Panel 1"),
      dockViewOutput("dock"),
      h1("Panels with different groups"),
      actionButton("move2", "Move Panel 1"),
      dockViewOutput("dock2"),
    )

    server <- function(input, output, session) {
      dock_proxy <- dock_view_proxy("dock")

      exportTestValues(
        panel_ids = get_panels_ids(dock_proxy),
        active_group = get_active_group(dock_proxy),
        grid = get_grid(dock_proxy)
      )

      output$dock <- renderDockView({
        dock_view(
          panels = list(
            panel(
              id = "1",
              title = "Panel 1",
              content = tagList(
                sliderInput(
                  "obs",
                  "Number of observations:",
                  min = 0,
                  max = 1000,
                  value = 500
                ),
                plotOutput("distPlot")
              )
            ),
            panel(
              id = "2",
              title = "Panel 2",
              content = tagList(
                selectInput(
                  "variable",
                  "Variable:",
                  c("Cylinders" = "cyl", "Transmission" = "am", "Gears" = "gear")
                ),
                tableOutput("data")
              ),
            ),
            panel(
              id = "3",
              title = "Panel 3",
              content = h1("Panel 3")
            )
          ),
          theme = "light-spaced"
        )
      })

      output$dock2 <- renderDockView({
        dock_view(
          panels = list(
            panel(
              id = "1",
              title = "Panel 1",
              content = "Panel 1"
            ),
            panel(
              id = "2",
              title = "Panel 2",
              content = "Panel 2",
              position = list(
                referencePanel = "1",
                direction = "within"
              )
            ),
            panel(
              id = "3",
              title = "Panel 3",
              content = h1("Panel 3"),
              position = list(
                referencePanel = "1",
                direction = "right"
              )
            )
          ),
          theme = "light-spaced"
        )
      })

      output$distPlot <- renderPlot({
        req(input$obs)
        hist(rnorm(input$obs))
      })
      output$data <- renderTable(
        {
          mtcars[, c("mpg", input$variable), drop = FALSE]
        },
        rownames = TRUE
      )

      observeEvent(input$move, {
        move_panel(
          dock_proxy,
          id = 1,
          index = 3
        )
      })

      dock_proxy2 <- dock_view_proxy("dock2")

      observeEvent(input$move2, {
        move_panel(
          dock_proxy2,
          id = 1,
          group = 3,
          position = "bottom"
        )
      })
    }

    shinyApp(ui, server)

## Dynamically move groups

You can move groups of panels using 2 different APIs described below.

### Group point of view

To move a group of panel(s), `move_group()` works by selecting the group source id, that is `from`, and the group target id, `to`. Position is relative to the `to`.

Toggle code

    library(shiny)
    library(dockViewR)

    options("dockViewR.mode" = "dev")

    ui <- fluidPage(
      actionButton(
        "move",
        "Move Group with group-id 1 at the bottom of group with group-id 3"
      ),
      dockViewOutput("dock"),
    )

    server <- function(input, output, session) {
      dock_proxy <- dock_view_proxy("dock")

      exportTestValues(
        panel_ids = get_panels_ids(dock_proxy),
        active_group = get_active_group(dock_proxy),
        grid = get_grid(dock_proxy)
      )
      output$dock <- renderDockView({
        dock_view(
          panels = list(
            panel(
              id = "1",
              title = "Panel 1",
              content = "Panel 1"
            ),
            panel(
              id = "2",
              title = "Panel 2",
              content = "Panel 2",
              position = list(
                referencePanel = "1",
                direction = "within"
              )
            ),
            panel(
              id = "3",
              title = "Panel 3",
              content = h1("Panel 3"),
              position = list(
                referencePanel = "1",
                direction = "right"
              )
            ),
            panel(
              id = "4",
              title = "Panel 4",
              content = h1("Panel 4"),
              position = list(
                referencePanel = "3",
                direction = "within"
              )
            ),
            panel(
              id = "5",
              title = "Panel 5",
              content = h1("Panel 5"),
              position = list(
                referencePanel = "4",
                direction = "right"
              )
            ),
            panel(
              id = "6",
              title = "Panel 6",
              content = h1("Panel 6"),
              position = list(
                referencePanel = "5",
                direction = "within"
              )
            )
          ),
          theme = "light-spaced"
        )
      })

      observeEvent(input$move, {
        move_group(
          dock_proxy,
          from = 1,
          to = 3,
          position = "bottom"
        )
      })
    }

    shinyApp(ui, server)

### Panel point of view

Another approach is possible with `move_group2`, which works from the point of view of a panel. This means given `from` which the panel id, `{dockViewR}` is able to find the group where it belongs to. Same for the `to`. This way you don’t have to worry about group ids, which are implicit.

Toggle code

    library(shiny)
    library(dockViewR)

    options("dockViewR.mode" = "dev")

    ui <- fluidPage(
      actionButton(
        "move",
        "Move Group that contains Panel 1 to the right of group
        that contains Panel 3"
      ),
      dockViewOutput("dock"),
    )

    server <- function(input, output, session) {
      dock_proxy <- dock_view_proxy("dock")

      exportTestValues(
        panel_ids = get_panels_ids(dock_proxy),
        active_group = get_active_group(dock_proxy),
        grid = get_grid(dock_proxy)
      )
      output$dock <- renderDockView({
        dock_view(
          panels = list(
            panel(
              id = "1",
              title = "Panel 1",
              content = "Panel 1"
            ),
            panel(
              id = "2",
              title = "Panel 2",
              content = "Panel 2",
              position = list(
                referencePanel = "1",
                direction = "within"
              )
            ),
            panel(
              id = "3",
              title = "Panel 3",
              content = h1("Panel 3"),
              position = list(
                referencePanel = "1",
                direction = "right"
              )
            ),
            panel(
              id = "4",
              title = "Panel 4",
              content = h1("Panel 4"),
              position = list(
                referencePanel = "3",
                direction = "within"
              )
            ),
            panel(
              id = "5",
              title = "Panel 5",
              content = h1("Panel 5"),
              position = list(
                referencePanel = "4",
                direction = "right"
              )
            ),
            panel(
              id = "6",
              title = "Panel 6",
              content = h1("Panel 6"),
              position = list(
                referencePanel = "5",
                direction = "within"
              )
            )
          ),
          theme = "light-spaced"
        )
      })

      observeEvent(input$move, {
        move_group2(
          dock_proxy,
          from = 1,
          to = 3,
          position = "right"
        )
      })
    }

    shinyApp(ui, server)

## Get the state of the dock

You can access the state of the dock which can return something like:

    dockViewR:::test_dock
    #> $grid
    #> $grid$root
    #> $grid$root$type
    #> [1] "branch"
    #>
    #> $grid$root$data
    #> $grid$root$data[[1]]
    #> $grid$root$data[[1]]$type
    #> [1] "leaf"
    #>
    #> $grid$root$data[[1]]$data
    #> $grid$root$data[[1]]$data$views
    #> $grid$root$data[[1]]$data$views[[1]]
    #> [1] "test"
    #>
    #> $grid$root$data[[1]]$data$views[[2]]
    #> [1] "2"
    #>
    #>
    #> $grid$root$data[[1]]$data$activeView
    #> [1] "2"
    #>
    #> $grid$root$data[[1]]$data$id
    #> [1] "1"
    #>
    #>
    #> $grid$root$data[[1]]$size
    #> [1] 95
    #>
    #>
    #> $grid$root$data[[2]]
    #> $grid$root$data[[2]]$type
    #> [1] "leaf"
    #>
    #> $grid$root$data[[2]]$data
    #> $grid$root$data[[2]]$data$views
    #> $grid$root$data[[2]]$data$views[[1]]
    #> [1] "3"
    #>
    #>
    #> $grid$root$data[[2]]$data$activeView
    #> [1] "3"
    #>
    #> $grid$root$data[[2]]$data$id
    #> [1] "2"
    #>
    #>
    #> $grid$root$data[[2]]$size
    #> [1] 95
    #>
    #>
    #>
    #> $grid$root$size
    #> [1] 0
    #>
    #>
    #> $grid$width
    #> [1] 0
    #>
    #> $grid$height
    #> [1] 0
    #>
    #> $grid$orientation
    #> [1] "HORIZONTAL"
    #>
    #>
    #> $panels
    #> $panels$`2`
    #> $panels$`2`$id
    #> [1] "2"
    #>
    #> $panels$`2`$contentComponent
    #> [1] "default"
    #>
    #> $panels$`2`$params
    #> $panels$`2`$params$content
    #> $panels$`2`$params$content$head
    #> [1] ""
    #>
    #> $panels$`2`$params$content$singletons
    #> list()
    #>
    #> $panels$`2`$params$content$dependencies
    #> list()
    #>
    #> $panels$`2`$params$content$html
    #> [1] "Panel 2"
    #>
    #>
    #> $panels$`2`$params$id
    #> [1] "2"
    #>
    #>
    #> $panels$`2`$title
    #> [1] "Panel 2"
    #>
    #>
    #> $panels$`3`
    #> $panels$`3`$id
    #> [1] "3"
    #>
    #> $panels$`3`$contentComponent
    #> [1] "default"
    #>
    #> $panels$`3`$params
    #> $panels$`3`$params$content
    #> $panels$`3`$params$content$head
    #> [1] ""
    #>
    #> $panels$`3`$params$content$singletons
    #> list()
    #>
    #> $panels$`3`$params$content$dependencies
    #> list()
    #>
    #> $panels$`3`$params$content$html
    #> [1] "<h1>Panel 3</h1>"
    #>
    #>
    #> $panels$`3`$params$id
    #> [1] "3"
    #>
    #>
    #> $panels$`3`$title
    #> [1] "Panel 3"
    #>
    #>
    #> $panels$test
    #> $panels$test$id
    #> [1] "test"
    #>
    #> $panels$test$contentComponent
    #> [1] "default"
    #>
    #> $panels$test$params
    #> $panels$test$params$content
    #> $panels$test$params$content$head
    #> [1] ""
    #>
    #> $panels$test$params$content$singletons
    #> list()
    #>
    #> $panels$test$params$content$dependencies
    #> list()
    #>
    #> $panels$test$params$content$html
    #> [1] "Panel 1"
    #>
    #>
    #> $panels$test$params$id
    #> [1] "test"
    #>
    #>
    #> $panels$test$title
    #> [1] "Panel 1"
    #>
    #>
    #>
    #> $activeGroup
    #> [1] "2"

The dock state is a deeply nested list:

    str(dockViewR:::test_dock)
    #> List of 3
    #>  $ grid       :List of 4
    #>   ..$ root       :List of 3
    #>   .. ..$ type: chr "branch"
    #>   .. ..$ data:List of 2
    #>   .. .. ..$ :List of 3
    #>   .. .. .. ..$ type: chr "leaf"
    #>   .. .. .. ..$ data:List of 3
    #>   .. .. .. .. ..$ views     :List of 2
    #>   .. .. .. .. .. ..$ : chr "test"
    #>   .. .. .. .. .. ..$ : chr "2"
    #>   .. .. .. .. ..$ activeView: chr "2"
    #>   .. .. .. .. ..$ id        : chr "1"
    #>   .. .. .. ..$ size: int 95
    #>   .. .. ..$ :List of 3
    #>   .. .. .. ..$ type: chr "leaf"
    #>   .. .. .. ..$ data:List of 3
    #>   .. .. .. .. ..$ views     :List of 1
    #>   .. .. .. .. .. ..$ : chr "3"
    #>   .. .. .. .. ..$ activeView: chr "3"
    #>   .. .. .. .. ..$ id        : chr "2"
    #>   .. .. .. ..$ size: int 95
    #>   .. ..$ size: int 0
    #>   ..$ width      : int 0
    #>   ..$ height     : int 0
    #>   ..$ orientation: chr "HORIZONTAL"
    #>  $ panels     :List of 3
    #>   ..$ 2   :List of 4
    #>   .. ..$ id              : chr "2"
    #>   .. ..$ contentComponent: chr "default"
    #>   .. ..$ params          :List of 2
    #>   .. .. ..$ content:List of 4
    #>   .. .. .. ..$ head        : chr ""
    #>   .. .. .. ..$ singletons  : list()
    #>   .. .. .. ..$ dependencies: list()
    #>   .. .. .. ..$ html        : chr "Panel 2"
    #>   .. .. ..$ id     : chr "2"
    #>   .. ..$ title           : chr "Panel 2"
    #>   ..$ 3   :List of 4
    #>   .. ..$ id              : chr "3"
    #>   .. ..$ contentComponent: chr "default"
    #>   .. ..$ params          :List of 2
    #>   .. .. ..$ content:List of 4
    #>   .. .. .. ..$ head        : chr ""
    #>   .. .. .. ..$ singletons  : list()
    #>   .. .. .. ..$ dependencies: list()
    #>   .. .. .. ..$ html        : chr "<h1>Panel 3</h1>"
    #>   .. .. ..$ id     : chr "3"
    #>   .. ..$ title           : chr "Panel 3"
    #>   ..$ test:List of 4
    #>   .. ..$ id              : chr "test"
    #>   .. ..$ contentComponent: chr "default"
    #>   .. ..$ params          :List of 2
    #>   .. .. ..$ content:List of 4
    #>   .. .. .. ..$ head        : chr ""
    #>   .. .. .. ..$ singletons  : list()
    #>   .. .. .. ..$ dependencies: list()
    #>   .. .. .. ..$ html        : chr "Panel 1"
    #>   .. .. ..$ id     : chr "test"
    #>   .. ..$ title           : chr "Panel 1"
    #>  $ activeGroup: chr "2"

On the top level it has 3 elements:

- grid: a list representing the dock layout.
- panels: a list having the same structure as `panel()` composing the dock.
- activeGroup: the current active group (a string).

Within the Shiny server function, on can access the state of the dock with `get_dock()`, passing the dock id (since the app may have multiple docks).

Each other function allows to deep dive into the returned value of `get_dock()`:

- `get_panels()` returns the panels element of `get_dock()`.
  - `get_panels_ids()` returns a character vector containing all panel ids from `get_panels()`.
- `get_active_group()` extracts the activeGroup component of `get_dock()` as a string.
- `get_grid()` returns the grid element of `get_dock()` which is a list. -`get_groups()` returns a list of panel groups from `get_grid()`.
  - `get_groups_ids()` returns a character vector of groups ids from `get_groups()`.
  - `get_groups_panels()` returns a list of character vector containing the ids of each panel within each group.

`save_dock()` and `restore_dock()` are used for their side effect to allow to respectively serialise and restore a dock object, as shown in the following demonstration app.

Each time a panel moves, or a group is maximized, the dock state is updated.

Toggle code

    library(shiny)
    library(bslib)
    library(dockViewR)
    library(listviewer)

    ui <- fluidPage(
      h1("Serialise dock state"),
      div(
        class = "d-flex justify-content-center",
        actionButton("save", "Save layout"),
        actionButton("restore", "Restore saved layout"),
        selectInput("states", "Select a state", NULL)
      ),
      dockViewOutput("dock"),
      reactjsonOutput("dock_state"),
    )

    server <- function(input, output, session) {
      output$dock_state <- renderReactjson({
        reactjson(jsonlite::toJSON(input$dock_state))
      })

      dock_states <- reactiveVal(NULL)

      dock_proxy <- dock_view_proxy("dock")

      observeEvent(input$save, {
        save_dock(dock_proxy)
        states <- c(dock_states(), list(input$dock_state))
        dock_states(setNames(states, seq_along(states)))
      })

      exportTestValues(
        n_states = length(dock_states()),
        panel_ids = get_panels_ids(dock_proxy),
        group_ids = get_groups_ids(dock_proxy),
        active_group = get_active_group(dock_proxy),
        active_views = get_active_views(dock_proxy),
        active_panel = get_active_panel(dock_proxy),
        grid = get_grid(dock_proxy)
      )

      observeEvent(dock_states(), {
        updateSelectInput(session, "states", choices = names(dock_states()))
      })

      observeEvent(input$restore, {
        if (!length(dock_states())) {
          showNotification("No saved states", type = "error")
          return(NULL)
        }
        restore_dock(dock_proxy, dock_states()[[input$states]])
      })

      output$dock <- renderDockView({
        dock_view(
          panels = list(
            panel(
              id = "test",
              title = "Panel 1",
              content = tagList(
                sliderInput(
                  "obs",
                  "Number of observations:",
                  min = 0,
                  max = 1000,
                  value = 500
                ),
                plotOutput("distPlot")
              )
            ),
            panel(
              id = 2,
              title = "Panel 2",
              content = "Panel 2",
              position = list(
                referencePanel = "test",
                direction = "within"
              )
            ),
            panel(
              id = 3,
              title = "Panel 3",
              content = h1("Panel 3"),
              position = list(
                referencePanel = "test",
                direction = "right"
              )
            )
          ),
          theme = "light-spaced"
        )
      })

      output$distPlot <- renderPlot({
        req(input$obs)
        hist(rnorm(input$obs))
      })
    }

    shinyApp(ui, server)