Q:

use flextable::display() in a function

I am trying to use the flextable::display() function from within a function, using the arguments from the function within display. Below is my function:
add_footnote <- function(df, col, pattern, symbol){

  tmp <- df
  pat <- paste0(pattern, " {{x}}")

  tmp <- display(tmp, 
                 col_key = col,
                 i = ~ col == pattern, 
                 pattern = pat,
                 formatters = list(x ~ as.character(symbol)),
                 fprops = list(x = fp_text(vertical.align = 'superscript')) ) 
  return(tmp)
}

# Call function
df <- regulartable(head(iris))
add_footnote(df, col = 'Species', pattern = 'setosa', symbol = 'a')

I'm hoping to get a superscript a wherever setosa appears in the Species column, however it gives the following error indicating that the display function can't see the arguments being passed to the function:

Error in eval(as.call(f[[2]]), envir = data) : object 'pattern' not found

Does anyone know how to get the arguments from the function to be recognised by the internal display() function?

A:

The function display is quite hard to use - that's why I wrote flextable::compose. It can rely on tidy eval syntax. Below 2 examples that should help you:
library(flextable)
library(officer)
library(rlang)

add_footnote_with_rlang <- function(df, col, pattern, symbol){
  form_ <- sprintf("~ %s == '%s'", col, pattern)
  colname <- enquo(col)
  flextable::compose(
    x = df, j = col, i = as.formula(form_), 
    value = as_paragraph(
      as_chunk(!!colname), 
      as_chunk(symbol, props = fp_text(vertical.align = 'superscript')))
    ) 
}
add_footnote <- function(df, col, pattern, symbol){
  form_ <- sprintf("~ %s == '%s'", col, pattern)
  flextable::compose(
    x = df, j = col, i = as.formula(form_), 
    value = as_paragraph(
      as_chunk(symbol, props = fp_text(vertical.align = 'superscript')))
    ) 
}

# Call function
df <- regulartable(head(iris))
# df <- add_footnote(df, col = 'Species', pattern = 'setosa', symbol = 'a')
df <- add_footnote_with_rlang(df, col = 'Species', pattern = 'setosa', symbol = 'a')
df

