Shiny: Dynamically subset data based on user column input

Question

I have a shiny application that allows the user to subset a data frame by selecting a column name from a dropdown list and assign a value to it. In the snippet below, df1 is a dataframe and if the user selects "country" from the dropdown and enters "UK" in the textbox, the temporary df, temp_dat should have only values of UK in it. For some reason that I cannot understand it states that 0 rows of 3 cols have been returned. Can somebody help me with this? Thanks in advance.

library(shinydashboard)
ui = dashboardPage(dashboardHeader(),
                   dashboardSidebar(),
                   dashboardBody(uiOutput("subset_check1"), uiOutput("subsetbox1‌​")))

server = function(input, output, session)
{
  names = c("Jane", "Doe", "Job", "Right")
  emp_id = c(1000, 1001, 1002, 1003)
  country = c("UK", "UK", "UK", "US")
  df1 = data.frame(names, emp_id, country)
  file1_cols = colnames(df1)
  output$subset_check1 = renderUI(checkboxInput(
    "subcheck1",
    "Would you like to subset this dataset with a condition?"
  ))
  observe({
    if (!is.null(input$subcheck1))
    {
      if (input$subcheck1 == "TRUE")
      {
        #print("box was checked")
        output$subsetbox1 = renderUI(flowLayout(
          selectInput(
            "subsetbox1sel",
            "Select column:",
            choices = c(file1_cols),
            multiple = T
          ),
          textInput("subsetbox1text", "Enter value")
        ))
        observe({
          if (!is.null(input$subsetbox1sel))
          {
            if (!is.null(input$subsetbox1text))
            {
              cols_sel1 = as.character(input$subsetbox1sel)
              vals_sel1 = as.character(input$subsetbox1text)
              temp_dat = df1[df1$cols_sel1 == vals_sel1, ]
              print(temp_dat)
            }
          }
        })
      }
    }
  })
} 

Answer 1

Currently, there is no column named cols_sel1 in the dataframe. But you intend to pass its string literal value. Hence, do not use the dollar $ qualifier but a string to reference the column (i.e., use latter of below) especially since this cols_sel1 varies with user selection:

df$col
df['col']

So simply adjust your temp_dat line to:

temp_dat = df1[df1[cols_sel1]==vals_sel1,]