diff --git a/mpaer_functions.R b/mpaer_functions.R
index 9e382931be402969a8a341e6ee3c72d3b76ba6ee..866cce0815382f11c88adcff3cb5929ec4df678a 100644
--- a/mpaer_functions.R
+++ b/mpaer_functions.R
@@ -117,3 +117,10 @@ latin_square <- function(n_trat) {
     attr(design, "matrix") <- M
     return(design)
 }
+
+as_letters <- function(x) {
+    xs <- strsplit(trimws(as.character(x)), "")
+    xs <- lapply(xs, as.integer)
+    m <- max(unlist(xs))
+    sapply(xs, function(i) paste(rev(letters[m - i + 1]), collapse = ""))
+}