base Prelude Data.List GHC.List GHC.OldList, Cabal Distribution.Compat.Prelude.Internal, ghc GHC.Prelude

filter, applied to a predicate and a list,
returns the list of those elements that satisfy the predicate; i.e.,

filter p xs = [ x | x <- xs, p x]

>>> filter odd [1, 2, 3] [1,3]

filter (> "a") (fromList [(5,"a"), (3,"b")]) == singleton 3 "b" filter (> "x") (fromList [(5,"a"), (3,"b")]) == empty filter (< "a") (fromList [(5,"a"), (3,"b")]) == empty

filter (> "a") (fromList [(5,"a"), (3,"b")]) == singleton 3 "b" filter (> "x") (fromList [(5,"a"), (3,"b")]) == empty filter (< "a") (fromList [(5,"a"), (3,"b")]) == empty

The filter function takes a predicate `p`
and a sequence `xs` and returns a sequence of those elements
which satisfy the predicate.

Filter all keys/values that satisfy some predicate.

Drop elements which do not satisfy the predicate

Drop elements which do not satisfy the predicate

Drop elements which do not satisfy the predicate

unordered-containers Data.HashMap.Internal Data.HashMap.Internal.Strict Data.HashMap.Lazy Data.HashMap.Strict

Filter this map by retaining only elements which values
satisfy a predicate.

Filter this set by retaining only elements satisfying a
predicate.

filter (pure True) = cat filter (liftA2 (&&) p1 p2) = filter p1 >-> filter p2 filter f = mapMaybe (\a -> a <$ guard (f a))