How to execute a paste function inside a reactive dataframe? - r

Question

I am somewhat familiar with the paste() function in base R. I am trying to learn Shiny and reactivity and don't understand how to execute a paste() inside a reactive Shiny function.
In running the demo code at the bottom, this is what first appears in the rendered "Reactive results" panel:
choice subclass
1 A 1
2 A 1
3 A 2
4 B 1
5 B 3
I'd like to paste the row number of each row in front of each "choice" column element, followed by a "." and a space, so that the "Reactive results" panel output looks like this:
choice subclass
1 1. A 1
2 2. A 1
3 3. A 2
4 4. B 1
5 5. B 3
How would I execute a paste() in this reactive example?
Demo code:
library(shiny)
data <- data.frame(choice = c("A","A","A","B","B"),subclass = c(1,1,2,1,3))
ui <- fluidPage(
h5(strong("Base data frame:")),
verbatimTextOutput("data"),
radioButtons(inputId = "showData",
label = h5(strong("Multiply base DF subclass by factor of:")),
choiceNames = c('One','Two'),
choiceValues = c('One','Two'),
selected = 'One',
inline = TRUE
),
h5(strong("Reactive results:")),
verbatimTextOutput("choices1")
)
server <- function(input, output, session) {
output$data <- renderPrint(data)
rv <- reactiveValues(choices1=c())
observeEvent(input$showData, {
if(input$showData == 'One'){rv$choices1 <- data[]}
else {rv$choices1[,2] <- 2 * data[ ,2]}
}
)
output[["choices1"]] <- renderPrint({rv$choices1})
}
shinyApp(ui, server)

Answer 1

Your app looks a bit complicated to me. But as I don't know about your desired final result I stick with your code and only did some slight changes in your observeEvent to achieve your desired result:
library(shiny)
data <- data.frame(choice = c("A", "A", "A", "B", "B"), subclass = c(1, 1, 2, 1, 3))
ui <- fluidPage(
h5(strong("Base data frame:")),
verbatimTextOutput("data"),
radioButtons(
inputId = "showData",
label = h5(strong("Multiply base DF subclass by factor of:")),
choiceNames = c("One", "Two"),
choiceValues = c("One", "Two"),
selected = "One",
inline = TRUE
),
h5(strong("Reactive results:")),
verbatimTextOutput("choices1")
)
server <- function(input, output, session) {
output$data <- renderPrint(data)
rv <- reactiveValues(choices1 = c())
observeEvent(input$showData, {
rv$choices1 <- data
rv$choices1$choice <- paste0(row.names(rv$choices1), ". ", rv$choices1$choice)
if (input$showData == "Two") {
rv$choices1[, 2] <- 2 * rv$choices1[, 2]
}
})
output[["choices1"]] <- renderPrint({
rv$choices1
})
}
shinyApp(ui, server)
#>
#> Listening on http://127.0.0.1:4262

Answer 2

Suggested modifications, in two parts.
First,
use str_glue instead of paste, and mutate to modify the dataframe,
replace choiceNames and choiceValues with a single argument choices, as they are equal,
rewrite output[["choices1"]] as output$choices1,
use dataframe column by name rather than by index,
replace reactiveValues and observeEvent with a single reactive: reactivity is automatic, you don't have to reimplement it with an oberveEvent.
Here is the code:
library(shiny)
library(dplyr)
library(magrittr)
library(stringr)
data <- data.frame(choice = c("A", "A", "A", "B", "B"),
subclass = c(1, 1, 2, 1, 3))
ui <- fluidPage(
h5(strong("Base data frame:")),
verbatimTextOutput("data"),
radioButtons(inputId = "showData",
label = h5(strong("Multiply base DF subclass by factor of:")),
choices = c("One", "Two"),
selected = "One",
inline = TRUE
),
h5(strong("Reactive results:")),
verbatimTextOutput("choices1")
)
server <- function(input, output, session) {
output$data <- renderPrint(data)
rv <- reactive({
df <- data %>% mutate(choice = str_glue("{row_number()}. {choice}"))
if (input$showData == "Two") {
df %<>% mutate(subclass = 2 * subclass)
}
df
})
output$choices1 <- renderPrint(rv())
}
shinyApp(ui, server)
Second simplification: the reactive is useless as it's only used once, in renderPrint. So put everything in renderPrint. It's still reactive.
library(shiny)
library(dplyr)
library(magrittr)
library(stringr)
data <- data.frame(choice = c("A", "A", "A", "B", "B"),
subclass = c(1, 1, 2, 1, 3))
ui <- fluidPage(
h5(strong("Base data frame:")),
verbatimTextOutput("data"),
radioButtons(inputId = "showData",
label = h5(strong("Multiply base DF subclass by factor of:")),
choices = c("One", "Two"),
selected = "One",
inline = TRUE
),
h5(strong("Reactive results:")),
verbatimTextOutput("choices1")
)
server <- function(input, output, session) {
output$data <- renderPrint(data)
output$choices1 <- renderPrint({
df <- data %>% mutate(choice = str_glue("{row_number()}. {choice}"))
if (input$showData == "Two") {
df %<>% mutate(subclass = 2 * subclass)
}
df
})
}
shinyApp(ui, server)