dataframe - R Shiny: Rearrange columns based on inputwidget

Question

I'm doing a project where I need to select a specific variable from an uploaded dataset to be located in column 1. I have created an selectInput inputwidget that is suppose to specify which variable in the dataset that I want to be located in column 1, but I'm having trouble using this inputwidget.

Normally I would use a code like this to manually rearrange a specific variable:

df <- df[,c(names(df)[6],names(df)[-6])]

This will relocate the variable located in column 6 to column 1. Of course, this code only work if the desired variable is located in column 6, which will not be the case in every dataset.

Using subsetting, I can't just replace the "6" with the inputwidget, since subsetting doesn't work on characters (as far as I know). I would like to avoid using an numeric inputwidget to specify the location of the variable, since I think the variable name is easier for a user to select, especially in a large dataset.

What is the easiest way of doing this?

Here is the app. Note that right now, the selectInput widget doesn't do anything.

ui <- fluidPage(

  navbarPage(title = "Rearrange columns in shiny R",
             
             
             tabPanel("Upload file",
                      br(),
                      sidebarPanel(
                        fileInput(inputId = "file1", label="Upload file"),
                        textOutput("dataset_info"),
                        br(),
                        uiOutput("col_1"),
                        hr(),
                        checkboxInput(inputId ="header", label="header", value = TRUE),
                        checkboxInput(inputId ="stringAsFactors", label="stringAsFactors", value = TRUE),
                        radioButtons(inputId = "sep", label = "Seperator", choices = c(Comma=",",Semicolon=";",Tab="",Space=" "), selected = ","),
                        radioButtons(inputId = "disp", "Display", choices = c(Head = "head", All = "all"), selected = "head"),
                        
                      ), # End sidebarPanel
                      
                      mainPanel(
                        tableOutput("contents"),
                        textOutput("display_info")
                      )# End mainPanel
             ))) # EndtabPanel "upload file"

            

 
server <- function(input, output, session) { 
 
# Upload file content table
 get_file_or_default <- reactive({
   if (is.null(input$file1)) {
     
     paste("No file is uploaded yet, please select a file.")
     
   } else { 
     df <- read.csv(input$file1$datapath,
                    header = input$header,
                    sep = input$sep,
                    quote = input$quote)
     output$dataset_info <- renderText(paste(dim(df)[2],"variables,",dim(df)[1],"obsevations."))
     
     if(input$disp == "head") {
       output$display_info <- renderText(paste("Showing 18 out of",dim(df)[1],"obsevations..."))
       return(head(df, 18))
     }
     else {
       return(df)
     }
   }
 })
 output$contents <- renderTable(get_file_or_default())
 

# Select column 1 variable 
 output$col_1 <- renderUI({
   req(input$file1)
   if (is.null(input$file1)) {} else {
     df <- read.csv(input$file1$datapath,
                    header = input$header,
                    sep = input$sep,
                    quote = input$quote)
     
     selectInput(inputId = "col_1",
                 label= "Variable to be in column 1",
                 choices = names(df),
                 selected = names(df)[1])
   }
 })
}


shinyApp(ui, server)
 

question from:https://stackoverflow.com/questions/65846594/r-shiny-rearrange-columns-based-on-inputwidget

Answer 1

As Ben pointed out, the answer can be found here: Move a column to first position in a data frame

The "moveme" package is out of date, but the setdiff() function does the job.

This is what I ended up using:

df <- df[c(input$col_1, setdiff(names(df),input$col_1))]