How do I get rid of a certain column in R shiny?

Question

I want to remove columns by using selectInput in R shiny to select the column names. To do so, I built the function "removecolumn," which takes "nameofthecolumn" as a parameter and removes the specified column. I used observeEvent to call the function in server code, but it doesn't work and gives me the following error.

Could someone please assist me in resolving this issue, as well as point me to any resources where I may learn how to call dynamic column names into any server function?

Error

Warning: Error in removecolumn: unused argument (input$selectcolumn)

csv data

ID  Type   Range
21  A1 B1   100
22  C1 D1   200
23  E1 F1   300

Overview of the code Basically, the code accepts a CSV file as input and, depending on the issue, I use the "SplitColumns" and "Delete Rows" and "Replace Values" buttons in the app, however, I'd like to add another button called "Remove Column" now.

app.R

library(shiny)
library(reshape2)
#source('splitColumn_stack.R')
library(DT)
library(tibble)


###function for deleting the rows
splitColumn <- function(data, column_name) {
  newColNames <- c("Unmerged_type1", "Unmerged_type2")
  newCols <- colsplit(data[[column_name]], " ", newColNames)
  after_merge <- cbind(data, newCols)
  after_merge[[column_name]] <- NULL
  after_merge
}
###_______________________________________________
### function for inserting a new column

fillvalues <- function(data, values, columName){
  df_fill <- data
  vec <- strsplit(values, ",")[[1]]
  df_fill <- tibble::add_column(df_fill, newcolumn = vec, .after = columName)
  df_fill
}

##function for removing the colum
removecolumn <- function(nameofthecolumn){
  df[ , -which(names(df) %in% nameofthecolumn)]
  
}

### use a_splitme.csv for testing this program

ui <- fluidPage(
  sidebarLayout(
    sidebarPanel(
      fileInput("file1", "Choose CSV File", accept = ".csv"),
      checkboxInput("header", "Header", TRUE),
      actionButton("Splitcolumn", "SplitColumn"),
      selectInput(inputId='selectcolumn', label='select column', ''),
      actionButton("deleteRows", "Delete Rows"),
      textInput("textbox", label="Input the value to replace:"),
      actionButton("replacevalues", label = 'Replace values'),
      actionButton("removecolumn", "Remove Column")
    ),
    mainPanel(
      DTOutput("table1")
    )
  )
)

server <- function(session, input, output) {
  rv <- reactiveValues(data = NULL)
  
  observeEvent(input$file1, {
    file <- input$file1
    ext <- tools::file_ext(file$datapath)
    
    req(file)
    
    validate(need(ext == "csv", "Please upload a csv file"))
    
    rv$data <- read.csv(file$datapath, header = input$header)
    
    updateSelectInput(session, 'selectcolumn', 'select column', names(rv$data))
    
  })
  
  observeEvent(input$Splitcolumn, {
    rv$data <- splitColumn(rv$data, input$selectcolumn)
  })
  
  observeEvent(input$deleteRows,{
    if (!is.null(input$table1_rows_selected)) {
      rv$data <- rv$data[-as.numeric(input$table1_rows_selected),]
    }
  })
  
  output$table1 <- renderDT({
    rv$data
  })
  observeEvent(input$replacevalues, {
    rv$data <- fillvalues(rv$data, input$textbox, input$selectcolumn)
  })
  observeEvent(input$removecolumn, {
    rv$data <- removecolumn(rv$data,input$selectcolumn)
  })
}

shinyApp(ui, server)

Answer 1

You forgot the argument df in your function removecolumn:

##function for removing the column
removecolumn <- function(df, nameofthecolumn){
  df[ , -which(names(df) %in% nameofthecolumn)]
}