Added better observe example

04b_simple.R

@@ -0,0 +1,69 @@
+library(shiny)
+library(ggplot2)
+library(dplyr)
+library(tidyr)
+
+ui <- fluidPage(
+
+  fluidRow(
+    column(width = 12,
+           # Create input widget and place-hold outputs
+           sliderInput("sample_count", "How many times should we sample each population?",
+                       value = 10,
+                       min = 1,
+                       max = 500),
+           plotOutput("sample_plot"),
+           br(),
+           textOutput("max")
+    )
+  )
+)
+
+server <- function(input, output) {
+
+  # Initialize the reactive value at 0.
+  # The reactive value can store intermediate values
+  # while keeping them in "reactive context"
+  sample_max <- reactiveVal(0)
+
+  # When the sample data changes, it
+  # triggers the contents of the "observe" expression
+  # to run. The observe does not return a value like "render"
+  # expressions do.
+  observe({
+    new_max <- max(sample_dat()$measurement)
+    sample_max(max(new_max, sample_max()))
+  })
+
+  sample_dat <- reactive({
+    # Sample from two normal distributions with slightly different means
+    # The rowid is just a unique identifier to allow tidying
+    data.frame("rowid" = paste0("row", seq(1,input[["sample_count"]])),
+               "thicc bois" = rnorm(input$sample_count, 0, 1),
+               "chonkers" = rnorm(input$sample_count, 0.2, 1),
+               stringsAsFactors = FALSE,
+               check.names = FALSE) %>%
+      # "Tidy" the dataframe into "long" format for plotting
+      gather(population, measurement, -rowid)
+  })
+
+  output$sample_plot <- renderPlot({
+    # Plot the two populations
+    ggplot(sample_dat(), aes(x = population, y = measurement, fill = population)) +
+      geom_boxplot() +
+      geom_point(position = position_jitterdodge(0.5)) +
+      theme(axis.text = element_text(size = rel(2)),
+            axis.title = element_text(size = rel(2)),
+            legend.text = element_text(size = rel(1.5)),
+            legend.title = element_text(size = rel(1.5)))
+  })
+
+  output$max <- renderText({
+    paste0("All-session maximum measurement: ", sample_max())
+  })
+
+}
+
+# Run the application 
+shinyApp(ui = ui, server = server)
+