R Shiny - Part II

.title[
# R Shiny - Part II
]
.subtitle[
## Workshop on Data Visualization in R
]
.author[
### Lokesh Mano • 17-Apr-2023
]
.institute[
### NBIS, SciLifeLab
]

---

---

## Contents

* [Reactivity](#react)
* [Isolate reactivity](#isolate)
* [observeEvent()](#observe)
* [Updating Widgets](#updating)
* [Error Validation](#error)
* [Download Button](#download)
* [Modularizing reactivity](#module)

---

## Reactivity

---

## Reactivity

---

## Reactivity

---

## Reactivity

---

## Reactivity

---

## Reactivity

---

## Isolate reactivity

* Reactivity can be controlled.

* You will notice that as soon as you try to change the title, the histogram will update with new values

## Isolate reactivity

## Isolate reactivity

---

name:isolate4

## Isolate reactivity

---

name:observe

## observeEvent()

---

## Updating widgets

* Widgets can be updated once initialised.
* Add third argument **session** to server function

```
server=function(input,output,session) {}
```

* Example of a typical UI

```
ui=fluidPage(
  selectInput("select-input",label="selectInput",choices=c("A","B","C")),
  numericInput("numeric-input",label="numericInput",value=5,min=1,max=10),
  sliderInput("slider-input",label="sliderInput",value=5,min=1,max=10),
)
```

* Update functions can be used to update input widgets
* Reactive observer `observe({})` monitors for a conditional change

```
server=function(input,output,session) {
  observe({
    if(something) {
      updateSelectInput(session,"select-input",label="selectInput",choices=c("D","E","F"))
      updateNumericInput(session,"numeric-input",label="numericInput",value=10,min=1,max=10)
      updateSliderInput(session,"slider-input",label="sliderInput",value=8,min=1,max=10)
    }
  })
}
```

---

## Error validation

* Shiny returns an error with missing or incorrect values

```r
shinyApp(
ui=fluidPage(
 selectInput("data_input",label="Select data",
 choices=c("","mtcars","faithful","iris")),
 tableOutput("table_output")
),
server=function(input, output) {
 getdata <- reactive({ get(input$data_input,'package:datasets') })
 output$table_output <- renderTable({head(getdata())})
})
```
]]

* Errors can be handled in a controlled manner

* `validate()` can be used to check input
* `validate()` using `need()`

.pull-left-70[.limity100[
```
shinyApp(
ui=fluidPage(
 selectInput("data_input",label="Select data",
 choices=c("","mtcars","faithful","iris")),
 tableOutput("table_output")
),
server=function(input, output) {
 getdata <- reactive({ 
 validate(need(try(input$data_input),"Please select a data set"))
 get(input$data_input,'package:datasets') 
 })
 output$table_output <- renderTable({head(getdata())})
})
```
]]

* `validate()` using custom function

.pull-left-70[.limity100[
```
valfn <- function(x) if(is.null(x) | is.na(x) | x=="") return("Input data is incorrect.")
shinyApp(
ui=fluidPage(
 selectInput("data_input",label="Select data",
 choices=c("","mtcars","faithful","iris")),
 tableOutput("table_output")
),
server=function(input,output) {
 getdata <- reactive({ 
 validate(valfn(try(input$data_input)))
 get(input$data_input,'package:datasets')
 })
 output$table_output <- renderTable({head(getdata())})
})
```
]]

* `shiny::req()` checks input variable and silently stops execution

---

## Download • Data

* Add button and `downloadHandler()` function

```
shinyApp(
ui=fluidPage(
 selectInput("data_input",label="Select data",
 choices=c("mtcars","faithful","iris")),
 textOutput("text_output"),
 downloadButton("button_download","Download")
),
server=function(input, output) {
 getdata <- reactive({ get(input$data_input, 'package:datasets') })
 output$text_output <- renderText(paste0("Selected dataset: ",input$data_input))
 
 output$button_download <- downloadHandler(
 filename = function() {
 paste0(input$data_input,".csv")
 },
 content = function(file) {
 write.csv(getdata(),file,row.names=FALSE,quote=F)
 })
})
```

* Run in system browser if Rstudio browser doesn't work
* See usage of download buttons

---

## Download • Plots

```
shinyApp(
ui=fluidPage(
 selectInput("data_input",label="Select data",
 choices=c("mtcars","faithful","iris")),
 textOutput("text_output"),
 plotOutput("plot_output",width="400px"),
 downloadButton("button_download", "Download")
),
server=function(input, output) {
 getdata <- reactive({ get(input$data_input, 'package:datasets') })
 output$text_output <- renderText(paste0("Selected dataset: ",input$data_input))
 output$plot_output <- renderPlot({hist(getdata()[, 1])})
 
output$button_download <- downloadHandler(
 filename = function() {
 paste0(input$data_input,".png")
 },
 content = function(file) {
 png(file)
 hist(getdata()[, 1])
 dev.off()
 })
})
```

* Run in system browser if Rstudio browser doesn't work
* See usage of download buttons

---

## Modularizing Reactivity

---

# Thank you. Questions?

Slide courtesy: Roy Francis (NBIS, RaukR2021)

<hr>

Built on : 17-Apr-2023 at 14:28:36

2023 • [SciLifeLab](https://www.scilifelab.se/) • [NBIS](https://nbis.se/)
]