Add new columns to data frame from shiny app

[koppula]

Hello folks,

I have data frame which is having name, Salary, hike_percent. My requirement is add 3 (c1,c2,c3) columns to same data frame from shiny app UI by entering below formula.

1. c1= (salary * hike_percent)
2. c2= "Salary Hike"
   3.c3=100.35

All 3 columns trying to add one after one and same get displayed in data table. Below is the code developed. Unfortunately i am not able to achieve the scenario due to issue with "fun_newcolumns". Please help me to solve the problem.

library(shiny)
library(dplyr)
library(data.table)
library(DT)
library(shinyWidgets)

dt <- data.table('name' = c('AAA', 'BBB', 'CCC'),'Salary' = c(1000, 1500, 2500),'hike_percent' = c(0.10, 0.13, 0.25))

fun_newcolumns <- function(colname,formula) {
  tran <- as.character(colname)
  newv <- names(formula)
  data <- dplyr::mutate_(dt, .dots = setNames(tran, newv))
  data
  }

#dt2 <- fun_newcolumns(colname=c1,formula=Salary )

# UI
ui <- fluidPage(sidebarLayout(
  sidebarPanel( prettyCheckboxGroup(inputId = "columns",label = "exported list of columns",choices = unique(names(dt))
    )),
  mainPanel(
    br(),
    div(style = "display: inline-block;vertical-align:top left; width: 300px;", textInput("newcolumnname", "new column name")),
    div(style = "display: inline-block;vertical-align:top centered; width: 500px;", textInput("formula", "enter formula here")),
    div(style = "display: inline-block;vertical-align:top right; width: 100px;", actionButton("addnewcolumn", "Add new column")),
    uiOutput("renderui"),
    DT::DTOutput("data_tbl")
  )
))
#SERVER
server <- function(input, output, session)
{
  reactive_string <- eventReactive(input$addnewcolumn, { dt2 <- fun_newcolumns(input$colname,input$formula) })
  output$renderui <- renderUI({ reactive_string() })
  reactive_string2 <- eventReactive(input$addnewcolumn,{ dt2  })
  output$data_tbl <- DT::renderDT({ reactive_string2() })
}
#Run the Shiny App to Display Webpage
shinyApp(ui = ui, server = server)