generalization of tidyr::unite

merge_chr.R

df <- tribble(
  ~ID, ~d1, ~d2, ~d3,
  1, "G", "G", "C",
  2, NA, "G", "T",
  3, "A", NA, "G",
  4, "G", "A", "A",
  5,  NA,  NA, NA,
  6, "G", "G", "G")

merge_chr <- function(df, col, ..., fun, remove = TRUE) {
  to_merge <- quos(...)
  col_name <- quo_name(enquo(col))

  merged <- dplyr::mutate(df,  !!col_name := pmap_chr(list(!!!to_merge), fun))
  if (remove) merged <- dplyr::select(merged, -one_of(map_chr(to_merge, quo_name)))
  merged
}

merge_chr(df, new, d1, d2, d3, fun = paste0)

first_non_na <- function(..., replacement) {
  x <- list(...)
  if (all(is.na(x))) return(replacement)
  x[[min(which(!is.na(x)))]]
}

non_na <- purrr::partial(first_non_na, replacement = "*")

merge_chr(df, new, d1, d2, d3, fun = non_na)