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="\t",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)

Would one of the options [in this post](https://stackoverflow.com/questions/22286419/move-a-column-to-first-position-in-a-data-frame) be helpful for you? — Ben, Jan 22 '21 at 14:07
This works, thanks! Although his "moveme" package seem to be outdated, the example using the setdiff() function works perfectly, as it allows for the inputwidget to be used as an argument. — Sound, Jan 22 '21 at 14:20

score 0 · Answer 1 · answered Jan 22 '21 at 14:23

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))]

R Shiny: Rearrange columns based on inputwidget

1 Answers1