box list element scalar atomic values (#1005)

- consistent representation as array-of-arrays, rather than
  array-arrays or scalars
- closes #1004

DESCRIPTION

@@ -1,7 +1,7 @@
 Package: DT
 Type: Package
 Title: A Wrapper of the JavaScript Library 'DataTables'
-Version: 0.23.1
+Version: 0.23.2
 Authors@R: c(
     person("Yihui", "Xie", email = "xie@yihui.name", role = c("aut", "cre")),
     person("Joe", "Cheng", role = "aut"),

NEWS.md

@@ -2,6 +2,8 @@
 
 - Fixed a bug with missing numeric values rendered as `0` (thanks, @tverbeke, #1000).
 
+- Box scalar elements of 'list' columns so that, e.g., `data.frame(col = I(integer(), 1, 2:3))` is represented in JavaScript as `[[], [1], [2, 3]]` instead of `[[], 1, [2, 3]]` (thanks, @mtmorgan, #1005).
+
 # CHANGES IN DT VERSION 0.23
 
 - Make sure number inputs return numeric values when editing numeric table cells (thanks, @stla, #987).

R/datatables.R

@@ -234,6 +234,9 @@ datatable = function(
   # applied to the "original" column names, instead of the "modified“ ones, e.g., via the `colnames` arg
   options[["columnDefs"]] = colDefsTgtHandle(options[["columnDefs"]], base::colnames(data))
 
+  # box scalar elements of list columns
+  data = boxListColumnAtomicScalars(data)
+
   # align numeric columns to the right
   if (length(numc)) {
     # if the `className` of the column has already been defined by the user,

R/utils.R

@@ -38,6 +38,25 @@ captionString = function(caption) {
   if (length(caption)) caption
 }
 
+# 'box' list column atomic scalars so that the data are represented
+# consistently (as arrays) in javascript, e.g.,
+# data.frame(col = I(list(integer(), 1, 2:3))) --> [[], [1], [2, 3]]
+# instead of [[], 1, [2, 3]]
+boxAtomicScalarElements = function(x) {
+  is_atomic = vapply(x, is.atomic, logical(1))
+  if (all(is_atomic)) {
+    is_scalar = lengths(x) == 1L
+    x[is_scalar] = lapply(x[is_scalar], list)
+  }
+  x
+}
+
+boxListColumnAtomicScalars = function(x) {
+  is_list = vapply(x, is.list, logical(1))
+  x[is_list] = lapply(x[is_list], boxAtomicScalarElements)
+  x
+}
+
 toJSON = function(...) {
   FUN = getFromNamespace('toJSON', 'htmlwidgets')
   FUN(...)