Add sortByName function

R/utils.R

@@ -206,6 +206,20 @@ mergeVectors <- function(a, b) {
   x[!drop_idx]
 }
 
+# Sort a vector by the names of items. If there are multiple items with the
+# same name, preserve the original order of those items. For empty
+# vectors/lists/NULL, return the original value.
+sortByName <- function(x) {
+  if (anyUnnamed(x))
+    stop("All items must be named")
+
+  # Special case for empty vectors/lists, and NULL
+  if (length(x) == 0)
+    return(x)
+
+  x[order(names(x))]
+}
+
 # Wrapper around list2env with a NULL check. In R <3.2.0, if an empty unnamed
 # list is passed to list2env(), it errors. But an empty named list is OK. For
 # R >=3.2.0, this wrapper is not necessary.

tests/testthat/test-utils.R

@@ -129,6 +129,31 @@ test_that("anyUnnamed works as expected", {
   expect_true(anyUnnamed(x))
 })
 
+test_that("sortByName works as expected", {
+  # Error if any unnamed elements
+  expect_error(sortByName(c("a", "b")))
+  expect_error(sortByName(list(a=1, 2)))
+
+  expect_identical(sortByName(NULL), NULL)
+  expect_identical(sortByName(numeric(0)), numeric(0))
+  expect_identical(sortByName(character(0)), character(0))
+  # Empty unnamed list
+  expect_identical(sortByName(list()), list())
+  # Empty named list
+  expect_identical(sortByName(list(a=1)[0]), list(a=1)[0])
+
+  expect_identical(sortByName(list(b=1, a=2)), list(a=2, b=1))
+  expect_identical(sortByName(list(b=1)), list(b=1))
+
+  # Ties are resolved by using original order
+  expect_identical(sortByName(list(b=1, a=2, b=3)), list(a=2, b=1, b=3))
+  expect_identical(sortByName(list(b=3, a=2, b=1)), list(a=2, b=3, b=1))
+
+  # Make sure atomic vectors work
+  expect_identical(sortByName(c(b=1, a=2)), c(a=2, b=1))
+  expect_identical(sortByName(c(b=1, a=2, b=3)), c(a=2, b=1, b=3))
+})
+
 test_that("Callbacks fire in predictable order", {
   cb <- Callbacks$new()