feat: add compact (#129)

* feat: add compact

* docs: missing document

NAMESPACE

@@ -63,6 +63,7 @@ export(chunk_vector)
 export(cite_bib)
 export(clbk)
 export(clbks)
+export(compact)
 export(compose)
 export(compute_mode)
 export(count_missing)

R/purrr_map.R

@@ -13,6 +13,7 @@
 #' * `map_at()` applies `.f` to each element of `.x` referenced by `.at`. All other elements remain unchanged.
 #' * `keep()` keeps those elements of `.x` where predicate `.p` evaluates to `TRUE`.
 #' * `discard()` discards those elements of `.x` where predicate `.p` evaluates to `TRUE`.
+#' * `compact()` discards elements of `.x` that are `NULL`.
 #' * `every()` is `TRUE` if predicate `.p` evaluates to `TRUE` for each `.x`.
 #' * `some()` is `TRUE` if predicate `.p` evaluates to `TRUE` for at least one `.x`.
 #' * `detect()` returns the first element where predicate `.p` evaluates to `TRUE`.
@@ -272,6 +273,12 @@ discard.data.table = function(.x, .p, ...) { # nolint
   .x[, is.na(.sel) | !.sel, with = FALSE]
 }
 
+#' @export
+#' @rdname compat-map
+compact = function(.x) { # nolint
+  .x[as.logical(lengths(.x))]
+}
+
 #' @export
 #' @rdname compat-map
 map_if = function(.x, .p, .f, ...) {

tests/testthat/test_map.R

@@ -201,6 +201,15 @@ test_that("detect", {
   expect_null(out)
 })
 
+test_that("compact", {
+  x = list(a = 1:3, b = c("a", "b"), c = NULL, d = NULL)
+  out = compact(x)
+  expect_identical(out, x[1:2])
+  x = list(a = 1:3, b = c("a", "b"), c = runif(3))
+  out = compact(x)
+  expect_identical(out, x)
+})
+
 test_that("pmap does not segfault (#56)", {
   expect_error(pmap(1:4, function(x) x), "list")
 })