diff options
Diffstat (limited to 'lib')
-rw-r--r-- | lib/default.nix | 2 | ||||
-rw-r--r-- | lib/lists.nix | 50 | ||||
-rw-r--r-- | lib/tests/misc.nix | 27 |
3 files changed, 77 insertions, 2 deletions
diff --git a/lib/default.nix b/lib/default.nix index c74c930233d5c..d5d47defb8e64 100644 --- a/lib/default.nix +++ b/lib/default.nix @@ -89,7 +89,7 @@ let recurseIntoAttrs dontRecurseIntoAttrs cartesianProduct cartesianProductOfSets mapCartesianProduct updateManyAttrsByPath; inherit (self.lists) singleton forEach foldr fold foldl foldl' imap0 imap1 - concatMap flatten remove findSingle findFirst any all count + ifilter0 concatMap flatten remove findSingle findFirst any all count optional optionals toList range replicate partition zipListsWith zipLists reverseList listDfs toposort sort sortOn naturalSort compareLists take drop sublist last init crossLists unique allUnique intersectLists diff --git a/lib/lists.nix b/lib/lists.nix index 28fa277b22b1f..ca436d7a9c94b 100644 --- a/lib/lists.nix +++ b/lib/lists.nix @@ -4,7 +4,7 @@ { lib }: let inherit (lib.strings) toInt; - inherit (lib.trivial) compare min id warn; + inherit (lib.trivial) compare min id warn pipe; inherit (lib.attrsets) mapAttrs; in rec { @@ -334,6 +334,54 @@ rec { imap1 = f: list: genList (n: f (n + 1) (elemAt list n)) (length list); /** + Filter a list for elements that satisfy a predicate function. + The predicate function is called with both the index and value for each element. + It must return `true`/`false` to include/exclude a given element in the result. + This function is strict in the result of the predicate function for each element. + This function has O(n) complexity. + + Also see [`builtins.filter`](https://nixos.org/manual/nix/stable/language/builtins.html#builtins-filter) (available as `lib.lists.filter`), + which can be used instead when the index isn't needed. + + # Inputs + + `ipred` + + : The predicate function, it takes two arguments: + - 1. (int): the index of the element. + - 2. (a): the value of the element. + + It must return `true`/`false` to include/exclude a given element from the result. + + `list` + + : The list to filter using the predicate. + + # Type + ``` + ifilter0 :: (int -> a -> bool) -> [a] -> [a] + ``` + + # Examples + :::{.example} + ## `lib.lists.ifilter0` usage example + + ```nix + ifilter0 (i: v: i == 0 || v > 2) [ 1 2 3 ] + => [ 1 3 ] + ``` + ::: + */ + ifilter0 = + ipred: + input: + map (idx: elemAt input idx) ( + filter (idx: ipred idx (elemAt input idx)) ( + genList (x: x) (length input) + ) + ); + + /** Map and concatenate the result. # Type diff --git a/lib/tests/misc.nix b/lib/tests/misc.nix index cf4a185c14689..6774939023d20 100644 --- a/lib/tests/misc.nix +++ b/lib/tests/misc.nix @@ -63,8 +63,10 @@ let hasAttrByPath hasInfix id + ifilter0 isStorePath lazyDerivation + length lists listToAttrs makeExtensible @@ -651,6 +653,31 @@ runTests { expected = ["b" "c"]; }; + testIfilter0Example = { + expr = ifilter0 (i: v: i == 0 || v > 2) [ 1 2 3 ]; + expected = [ 1 3 ]; + }; + testIfilter0Empty = { + expr = ifilter0 (i: v: abort "shouldn't be evaluated!") [ ]; + expected = [ ]; + }; + testIfilter0IndexOnly = { + expr = length (ifilter0 (i: v: mod i 2 == 0) [ (throw "0") (throw "1") (throw "2") (throw "3")]); + expected = 2; + }; + testIfilter0All = { + expr = ifilter0 (i: v: true) [ 10 11 12 13 14 15 ]; + expected = [ 10 11 12 13 14 15 ]; + }; + testIfilter0First = { + expr = ifilter0 (i: v: i == 0) [ 10 11 12 13 14 15 ]; + expected = [ 10 ]; + }; + testIfilter0Last = { + expr = ifilter0 (i: v: i == 5) [ 10 11 12 13 14 15 ]; + expected = [ 15 ]; + }; + testFold = let f = op: fold: fold op 0 (range 0 100); |