Test whether functions preserve names (cf #575).

Principles:

- Preserve names where the output has a 1-to-1 correspondence with the input.
- Preserve names for functions where base behavior suggests keeping names (e.g., grepl/grep(value=TRUE), sort/unique).
- Source of names: use names from the primary `string` argument only; ignore names on `pattern`/`replacement`/others and never merge.
- For 1-row-per-input matrices/lists (e.g., str_locate/str_match/str_split_fixed), set row/list names from input names.
- Don't preserve names where strings are combined, or the return values are indices
  (e.g., str_c, str_flatten, str_glue, str_which, str_order, str_equal).

Currently passing:

- str_subset
- str_trunc

Currently failing:

- str_count
- str_detect
- str_starts
- str_ends
- str_like
- str_escape
- str_replace
- str_remove
- str_conv
- str_trim
- str_pad
- str_sub
- str_to_lower
- str_to_upper
- str_to_title
- str_extract
- str_locate
- str_match
- str_extract_all
- str_locate_all
- str_match_all
- str_split
- str_split_fixed
- str_split_i
- str_sub_all
- str_length
- str_width
- str_dup
- word
- str_unique
- str_replace_na
- str_sort
- str_wrap
- str_replace_all

Author: jonovik

tests/testthat/test-preserve-names.R

@@ -0,0 +1,89 @@
+x <- c(C = "3", B = "2", A = "1")
+
+test_that("elementwise logical/numeric functions preserve names", {
+
+  expect_equal(names(str_count(x, ".")), names(x))
+  expect_equal(names(str_detect(x, "[123]")), names(x))
+  expect_equal(names(str_starts(x, "1")), names(x))
+  expect_equal(names(str_ends(x, "1")), names(x))
+  expect_equal(names(str_like(x, "%")), names(x))
+})
+
+test_that("elementwise string transforms preserve names", {
+  expect_equal(names(str_escape(x)), names(x))
+  expect_equal(names(str_replace(x, "[0-9]", "x")), names(x))
+  expect_equal(names(str_replace_all(x, "[0-9]", "x")), names(x))
+  expect_equal(names(str_remove(x, "[0-9]")), names(x))
+  expect_equal(names(str_conv(x, "UTF-8")), names(x))
+  expect_equal(names(str_trim(x)), names(x))
+  expect_equal(names(str_trunc(x, 3)), names(x))
+  expect_equal(names(str_pad(x, 2, side = "left")), names(x))
+  expect_equal(names(str_sub(x, 1, 1)), names(x))
+})
+
+test_that("case conversions preserve names", {
+  expect_equal(names(str_to_lower(x)), names(x))
+  expect_equal(names(str_to_upper(x)), names(x))
+  expect_equal(names(str_to_title(x)), names(x))
+})
+
+test_that("extraction functions preserve names (vector)", {
+  expect_equal(names(str_extract(x, "[0-9]")), names(x))
+})
+
+test_that("location/match matrices preserve row names", {
+  expect_equal(rownames(str_locate(x, "[0-9]")), names(x))
+  expect_equal(rownames(str_match(x, "([0-9])")), names(x))
+})
+
+test_that("list/matrix outputs preserve names on outer structure", {
+  # Lists
+  expect_equal(names(str_extract_all(x, "[0-9]")), names(x))
+  expect_equal(names(str_locate_all(x, "[0-9]")), names(x))
+  expect_equal(names(str_match_all(x, "([0-9])")), names(x))
+  expect_equal(names(str_split(x, "")), names(x))
+  expect_equal(names(str_sub_all(x, 1, 1)), names(x))
+
+  # Matrices (rows correspond to inputs)
+  expect_equal(rownames(str_split(x, "", simplify = TRUE)), names(x))
+  expect_equal(rownames(str_split_fixed(x, "", 1)), names(x))
+})
+
+test_that("length and duplication preserve names", {
+  expect_equal(names(str_length(x)), names(x))
+  expect_equal(names(str_width(x)), names(x))
+  expect_equal(names(str_dup(x, 2)), names(x))
+})
+
+test_that("word() preserves names", {
+  expect_equal(names(word(x, 1)), names(x))
+})
+
+test_that("str_unique() preserves names of first occurrences", {
+  y <- c(A = "a", A2 = "a", B = "b")
+  out <- str_unique(y)
+  expect_equal(names(out), c("A", "B"))
+})
+
+test_that("str_replace_na() preserves names", {
+  y <- c(A = NA, B = "x")
+  expect_equal(names(str_replace_na(y)), names(y))
+})
+
+test_that("str_subset() preserves names of retained elements", {
+  out <- str_subset(x, "[12]")
+  expect_equal(names(out), c("B", "A"))
+})
+
+test_that("str_sort() preserves names", {
+  out <- str_sort(x)
+  expect_equal(names(out), c("A", "B", "C"))
+})
+
+test_that("str_wrap() preserves names", {
+  expect_equal(names(str_wrap(x)), names(x))
+})
+
+test_that("str_split_i() preserves names", {
+  expect_equal(names(str_split_i(x, " ", 1)), names(x))
+})