From 8fbda1cf2e1399b95179ef85bc34ac524f1e64a5 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Maximilian=20M=C3=BCcke?= <muecke.maximilian@gmail.com>
Date: Wed, 5 Feb 2025 21:58:27 +0100
Subject: [PATCH] feat: add compact (#129)

* feat: add compact

* docs: missing document
---
 NAMESPACE                 | 1 +
 R/purrr_map.R             | 7 +++++++
 man/compat-map.Rd         | 4 ++++
 tests/testthat/test_map.R | 9 +++++++++
 4 files changed, 21 insertions(+)

diff --git a/NAMESPACE b/NAMESPACE
index 7104f258..71be46d0 100644
--- a/NAMESPACE
+++ b/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)
diff --git a/R/purrr_map.R b/R/purrr_map.R
index 9f61d94b..71acd540 100644
--- a/R/purrr_map.R
+++ b/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, ...) {
diff --git a/man/compat-map.Rd b/man/compat-map.Rd
index 38dee256..020aabed 100644
--- a/man/compat-map.Rd
+++ b/man/compat-map.Rd
@@ -27,6 +27,7 @@
 \alias{imap_dtc}
 \alias{keep}
 \alias{discard}
+\alias{compact}
 \alias{map_if}
 \alias{map_if.default}
 \alias{map_at}
@@ -88,6 +89,8 @@ keep(.x, .f, ...)
 
 discard(.x, .p, ...)
 
+compact(.x)
+
 map_if(.x, .p, .f, ...)
 
 \method{map_if}{default}(.x, .p, .f, ...)
@@ -140,6 +143,7 @@ each vector of \code{.x}, then the second element of \code{.x}, and so on.
 \item \code{map_at()} applies \code{.f} to each element of \code{.x} referenced by \code{.at}. All other elements remain unchanged.
 \item \code{keep()} keeps those elements of \code{.x} where predicate \code{.p} evaluates to \code{TRUE}.
 \item \code{discard()} discards those elements of \code{.x} where predicate \code{.p} evaluates to \code{TRUE}.
+\item \code{compact()} discards elements of \code{.x} that are \code{NULL}.
 \item \code{every()} is \code{TRUE} if predicate \code{.p} evaluates to \code{TRUE} for each \code{.x}.
 \item \code{some()} is \code{TRUE} if predicate \code{.p} evaluates to \code{TRUE} for at least one \code{.x}.
 \item \code{detect()} returns the first element where predicate \code{.p} evaluates to \code{TRUE}.
diff --git a/tests/testthat/test_map.R b/tests/testthat/test_map.R
index 1e2f0b0e..7ce457a3 100644
--- a/tests/testthat/test_map.R
+++ b/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")
 })