Inputs and outputs

Case Studies: Building Web Applications with Shiny in R

Dean Attali

Shiny Consultant

Inputs

chapter1_2_inputs_and_outputs.005.png

Inputs

chapter1_2_inputs_and_outputs.006.png

Building inputs

ui <- fluidPage(
    textInput(inputId = "name", label = "Enter your name",
              value = "Dean"),
    numericInput(inputId = "sibs", label = "How many siblings?",
                 value = 4, min = 0)
)

Input functions: *Input(inputId, label, ...)
inputId = Unique ID
label = Text to describe input
... = Additional input-specific parameters

Outputs

Plots, tables, text - anything R creates & users see
Two steps:
1. Create placeholder for output (in UI)
```
ui <- fluidPage(
 "Plot goes here:",
 plotOutput(outputId = "my_plot")
)
```
2. Write R code to generate output (in server)

The server

server <- function(input, output) {

  # Code for building outputs

}

input
- Read values from here (inputs user modifies)
output
- Write values to here (outputs e.g. plots, tables)

Building outputs

ui <- fluidPage(
    numericInput("num", "Number of rows", value = 10, min = 0),
    tableOutput("my_table")
)

server <- function(input, output) {
    output$my_table <- renderTable({
        head(iris, n = input$num)
    })
}

3 Rules to build output object:
1. Build object inside render function (renderPlot(), renderText(), etc)
2. Save object to output$<outputId>
3. Use input$<inputId> to access value of input

Let's practice!

Case Studies: Building Web Applications with Shiny in R