solving exercises chapther 16 (#101)

examples/16-escaping_the_graph/16.3.4-exercises/01-exercise.R

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+
+# Provide a server function that draws a histogram of 100 random numbers
+#  from a normal distribution when normal is clicked, and 100 random uniforms.
+
+library(shiny)
+
+ui <- fluidPage(
+  actionButton("rnorm", "Normal"),
+  actionButton("runif", "Uniform"),
+  plotOutput("plot")
+)
+
+server <- function(input, output, session) {
+
+  values <- reactiveVal(vector(mode = "numeric"))
+
+  observeEvent(input$rnorm, values(rnorm(100)))
+
+  observeEvent(input$runif, values(runif(100)))
+
+  output$plot <- renderPlot({
+    req(input$rnorm | input$runif)
+    hist(values())
+  })
+}
+
+shinyApp(ui, server)
+
+# source: https://mastering-shiny-solutions.netlify.app/escaping-the-graph

examples/16-escaping_the_graph/16.3.4-exercises/02-exercise.R

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+
+# Modify your code from above for to work with this UI:
+
+library(shiny)
+
+ui <- fluidPage(
+  selectInput("type", "type", c("Normal", "Uniform")),
+  actionButton("go", "go"),
+  plotOutput("plot")
+)
+
+server <- function(input, output, session) {
+
+  values <- reactiveVal(vector(mode = "numeric"))
+
+  observeEvent(input$go, {
+    if(input$type == "Normal") values(rnorm(100)) else values(runif(100))
+  })
+
+  output$plot <- renderPlot({
+    req(input$go)
+    hist(values())
+  })
+}
+
+shinyApp(ui, server)
+
+# source: https://mastering-shiny-solutions.netlify.app/escaping-the-graph

examples/16-escaping_the_graph/16.3.4-exercises/03-exercise.R

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+
+# Rewrite your code from the previous answer to eliminate the use of 
+# observe()/observeEvent() and only use reactive().
+# Why can you do that for the second UI but not the first?
+
+# Now we just need to track the event go.
+
+library(shiny)
+
+ui <- fluidPage(
+  selectInput("type", "type", c("Normal", "Uniform")),
+  actionButton("go", "go"),
+  plotOutput("plot")
+)
+
+server <- function(input, output, session) {
+
+  values <- reactive({
+    if(input$go == 0) return(NULL)
+    if(input$type == "Normal"){
+      rnorm(100)
+    }else{
+      runif(100)
+    }
+  })
+
+  output$plot <- renderPlot({
+    if(is.null(values())) return(NULL)
+    hist(values())
+  })
+}
+
+shinyApp(ui, server)
+
+# source: https://mastering-shiny-solutions.netlify.app/escaping-the-graph