Shiny R: Modifying the variable class - r

Question

I am trying to create a shiny-app that load data-set, present the variable list and their classes and allow the user to modify the class of a selected variable. All the functions in the following code are working except to the last function in the server- observeEvent which not working when trying to modify the variable class. Any suggestions?
Thank you in advance,
Rami
`
rm(list = ls())
library(shiny)
library(shinydashboard)
library(DT)
ui <- dashboardPage(
dashboardHeader(title = "Shiny Example"),
#--------------------------------------------------------------------
dashboardSidebar(
sidebarMenu(
menuItem("Data", tabName = "data", icon = icon("th"))
)
),
#--------------------------------------------------------------------
dashboardBody(
#--------------------------------------------------------------------
tabItem(tabName = "data",
fluidPage(
fluidRow(
box(
selectInput('dataset', 'Select Dataset', list(GermanCredit = "GermanCredit",
cars = "cars",
iris = "iris")),
title = "Datasets",width = 4, status = "primary",
checkboxInput("select_all", "Select All Variable", value = TRUE),
conditionalPanel(condition = "input.select_all == false",
uiOutput("show.var"))
),
box(
title = "Variable Summary", width = 4, status = "primary",
DT::dataTableOutput('summary.data')
),
box(
title = "Modify the Variable Class", width = 4, status = "primary",
radioButtons("choose_class", label = "Modify the Variable Class",
choices = list(Numeric = "numeric", Factor = "factor",
Character = "character"),
selected = "numeric"),
actionButton("var_modify", "Modify")
)
)
)
)
)
)
#--------------------------------------------------------------------
# Server Function
#--------------------------------------------------------------------
server <- function(input, output,session) {
#--------------------------------------------------------------------
# loading the data
get.df <- reactive({
if(input$dataset == "GermanCredit"){
data("GermanCredit")
GermanCredit
}else if(input$dataset == "cars"){
data(cars)
cars
}else if(input$dataset == "iris"){
data("iris")
iris
}
})
# Getting the list of variable from the loaded dataset
var_list <- reactive(names(get.df()))
# Choosing the variable - checkbox option
output$show.var <- renderUI({
checkboxGroupInput('show_var', 'Select Variables', var_list(), selected = var_list())
})
# Setting the data frame based on the variable selction
df <- reactive({
if(input$select_all){
df <- get.df()
} else if(!input$select_all){
df <- get.df()[, input$show_var, drop = FALSE]
}
return(df)
})
# create list of variables
col.name <- reactive({
d <- data.frame(names(df()), sapply(df(),class))
names(d) <- c("Name", "Class")
return(d)
})
# render the variable list into table
output$summary.data <- DT::renderDataTable(col.name(), server = FALSE, rownames = FALSE,
selection = list(selected = 1, mode = 'single'),
options = list(lengthMenu = c(5, 10, 15, 20), pageLength = 20, dom = 'p'))
# storing the selected variable from the variables list table
table.sel <- reactive({
df()[,which(colnames(df()) == col.name()[input$summary.data_rows_selected,1])]
})
# Trying to modify the variable class
observeEvent(input$var_modify,{
modify.row <- which(colnames(df()) == col.name()[input$summary.data_rows_selected,1])
if( input$choose_class == "numeric"){
df()[, modify.row] <- as.numeric(df()[, modify.row])
} else if( input$choose_class == "factor"){
df()[, modify.row] <- as.factor(df()[, modify.row])
} else if( input$choose_class == "character"){
df()[, modify.row] <- as.character(df()[, modify.row])
}
})
}
shinyApp(ui = ui, server = server)
`

Answer 1

I would use reactiveValues() instead.
library(shiny)
# Define UI for application that draws a histogram
ui <- shinyUI(fluidPage(
sidebarLayout(
sidebarPanel(
selectInput("classType", "Class Type:", c("as.numeric", "as.character"))
),
mainPanel(
textOutput("class")
)
)
))
server <- shinyServer(function(input, output) {
global <- reactiveValues(sample = 1:9)
observe({
global$sample <- get(input$classType)(global$sample)
})
output$class <- renderText({
print(class(global$sample))
})
})
shinyApp(ui = ui, server = server)
In case you are interested:
Concerning your attempt: reactive() is a function and you called the output of the function by df()[, modify.row]. So in your code you try to change the output of the function, but that does not change the output of futures calls of that function.
Maybe it is easier to see in a simplified version:
mean(1:3) <- 1
The code can not change the mean function to output 1 in future. So thats what reactiveValues() help with :). Hope that helps!