Add empty_cells and unused_pairs functions. (#19)

DESCRIPTION

@@ -1,6 +1,6 @@
 Package: wallis
 Title: Room squares in R
-Version: 0.0.0.9002
+Version: 0.0.0.9003
 Authors@R: 
     person("Matthew", "Henderson", , "matthew.james.henderson@gmail.com", role = c("aut", "cre"),
            comment = c(ORCID = "0000-0001-7949-8208"))

NAMESPACE

@@ -1,5 +1,7 @@
 # Generated by roxygen2: do not edit by hand
 
+export(empty_cells)
 export(n_filled_cells)
 export(plot_room_square)
+export(unused_pairs)
 export(volume)

R/empty-cells.R

@@ -0,0 +1,11 @@
+#' Empty cells of a partial Room square
+#'
+#' @param R A partial Room square.
+#'
+#' @return A list of empty cells of R.
+#' @export
+empty_cells <- function(R) {
+  E <- R[is.na(R$first), ]
+  E <- mapply(c, E$row, E$col, SIMPLIFY = FALSE)
+  return(E)
+}

R/unused-pairs.R

@@ -0,0 +1,24 @@
+#' Pairs not used in a partial Room square
+#'
+#' @param R A partial Room square.
+#'
+#' @return A list of pairs not used in R.
+#' @export
+unused_pairs <- function(R) {
+
+  n <- max(R$row) + 1
+
+  used_pairs <- R |> dplyr::select(first, second)
+
+  x <- combn(0:(n - 1), 2)
+
+  all_pairs <- tibble::tibble(
+     first = x[1,],
+    second = x[2,]
+  )
+
+  dplyr::anti_join(all_pairs, used_pairs, by = c("first", "second")) |>
+    dplyr::mutate(ffs = purrr::map2(first, second, c)) |>
+    dplyr::pull(ffs)
+
+}