library(shiny)
library(tidyverse)
library(shinydashboard)

data("mtcars")
source_data <- mtcars %>% as_tibble() %>% rownames_to_column(var = "model")
ui <- dashboardPage(
  dashboardHeader(title = "Hello Shiny!"),
  dashboardSidebar(
    checkboxGroupInput("liczba_cylindrow",
                       label = "Liczba cylindrów",
                       choices = setNames(unique(source_data$cyl), unique(source_data$cyl))
    )
  ),
  dashboardBody(
    fluidRow(
      box(width = 12,
          title = "Moc samochodów",
          plotOutput("wykres_moc"))
    )
  )
)
server <- function(input, output) {
  reactive_data <- reactive({
    req(length(input$liczba_cylindrow) > 0) # jeśli nic nie zaznaczono, to nie wykonuj
    data <-
      source_data %>%
      filter(cyl %in% input$liczba_cylindrow)
    return(data)
  })
  output$wykres_moc <- renderPlot({
    reactive_data() %>%
      ggplot(aes(x = hp)) + geom_histogram()
  })
}
shinyApp(ui = ui, server = server)