Add filter(f, ::Namedtuple) (#50795)

Author: aplavin

NEWS.md

@@ -102,6 +102,7 @@ New library features
   data-races. Or use the callback form of `open` to have all that handled
   automatically.
 * `@timed` now additionally returns the elapsed compilation and recompilation time ([#52889])
+* `filter` can now act on a `NamedTuple` ([#50795]).
 
 Standard library changes
 ------------------------

base/namedtuple.jl

@@ -268,6 +268,8 @@ function map(f, nt::NamedTuple{names}, nts::NamedTuple...) where names
     NamedTuple{names}(map(f, map(Tuple, (nt, nts...))...))
 end
 
+filter(f, xs::NamedTuple) = xs[filter(k -> f(xs[k]), keys(xs))]
+
 function merge_names(an::Tuple{Vararg{Symbol}}, bn::Tuple{Vararg{Symbol}})
     @nospecialize
     @_total_meta

test/namedtuple.jl

@@ -134,6 +134,14 @@ end
 @test map(string, (x=1, y=2)) == (x="1", y="2")
 @test map(round, (x=UInt, y=Int), (x=3.1, y=2//3)) == (x=UInt(3), y=1)
 
+@testset "filter" begin
+    @test filter(isodd, (a=1,b=2,c=3)) === (a=1, c=3)
+    @test filter(i -> true, (;)) === (;)
+    longnt = NamedTuple{ntuple(i -> Symbol(:a, i), 20)}(ntuple(identity, 20))
+    @test filter(iseven, longnt) === NamedTuple{ntuple(i -> Symbol(:a, 2i), 10)}(ntuple(i -> 2i, 10))
+    @test filter(x -> x<2, (longnt..., z=1.5)) === (a1=1, z=1.5)
+end
+
 @test merge((a=1, b=2), (a=10,)) == (a=10, b=2)
 @test merge((a=1, b=2), (a=10, z=20)) == (a=10, b=2, z=20)
 @test merge((a=1, b=2), (z=20,)) == (a=1, b=2, z=20)