Add insorted for in function in sorted arrays

NEWS.md

@@ -72,6 +72,7 @@ New library functions
 * New function `sincospi` for simultaneously computing `sinpi(x)` and `cospi(x)` more
   efficiently ([#35816]).
 * New function `addenv` for adding environment mappings into a `Cmd` object, returning the new `Cmd` object.
+* New function `insorted` for determining whether an element is in a sorted collection or not ([#37490]).
 
 New library features
 --------------------

base/exports.jl

@@ -457,6 +457,7 @@ export
     searchsorted,
     searchsortedfirst,
     searchsortedlast,
+    insorted,
     startswith,
 
 # linear algebra

base/operators.jl

@@ -1063,7 +1063,8 @@ splat(f) = args->f(args...)
     in(x)
 
 Create a function that checks whether its argument is [`in`](@ref) `x`, i.e.
-a function equivalent to `y -> y in x`.
+a function equivalent to `y -> y in x`. See also [`insorted`](@ref) for the use
+in sorted collections.
 
 The returned function is of type `Base.Fix2{typeof(in)}`, which can be
 used to implement specialized methods.

base/sort.jl

@@ -27,6 +27,7 @@ export # also exported by Base
     searchsorted,
     searchsortedfirst,
     searchsortedlast,
+    insorted,
     # order & algorithm:
     sort,
     sort!,
@@ -407,6 +408,39 @@ julia> searchsortedlast([1, 2, 4, 5, 5, 7], 0) # no match, insert at start
 ```
 """ searchsortedlast
 
+"""
+    insorted(a, x; by=<transform>, lt=<comparison>, rev=false)
+
+Determine whether an item is in the given sorted collection, in the sense that
+it is [`==`](@ref) to one of the values of the collection according to the order
+specified by the `by`, `lt` and `rev` keywords, assuming that `a` is already
+sorted in that order, see [`sort`](@ref) for the keywords. See also
+[`in`](@ref). Returns a `Bool` value.
+
+# Examples
+```jldoctest
+julia> insorted(4, [1, 2, 4, 5, 5, 7]) # single match
+true
+
+julia> insorted(5, [1, 2, 4, 5, 5, 7]) # multiple matches
+true
+
+julia> insorted(3, [1, 2, 4, 5, 5, 7]) # no match
+false
+
+julia> insorted(9, [1, 2, 4, 5, 5, 7]) # no match
+false
+
+julia> insorted(0, [1, 2, 4, 5, 5, 7]) # no match
+false
+```
+
+!!! compat "Julia 1.6"
+     `insorted` was added in Julia 1.6.
+"""
+function insorted end
+insorted(x, v::AbstractVector; kw...) = !isempty(searchsorted(v, x; kw...))
+insorted(x, r::AbstractRange) = in(x, r)
 
 ## sorting algorithms ##
 

doc/src/base/sort.md

@@ -125,6 +125,7 @@ Base.issorted
 Base.Sort.searchsorted
 Base.Sort.searchsortedfirst
 Base.Sort.searchsortedlast
+Base.Sort.insorted
 Base.Sort.partialsort!
 Base.Sort.partialsort
 Base.Sort.partialsortperm

test/sorting.jl

@@ -299,6 +299,61 @@ Base.step(r::ConstantRange) = 0
         end
     end
 end
+@testset "insorted" begin
+    numTypes = [ Int8,  Int16,  Int32,  Int64,  Int128,
+                UInt8, UInt16, UInt32, UInt64, UInt128,
+                Float16, Float32, Float64, BigInt, BigFloat]
+
+    @test insorted(1, collect(1:10), by=(x -> x >= 5)) == true
+    @test insorted(10, collect(1:10), by=(x -> x >= 5)) == true
+
+    for R in numTypes, T in numTypes
+        @test insorted(T(0), R[1, 1, 2, 2, 3, 3]) === false
+        @test insorted(T(1), R[1, 1, 2, 2, 3, 3]) == true
+        @test insorted(T(2), R[1, 1, 2, 2, 3, 3]) == true
+        @test insorted(T(4), R[1, 1, 2, 2, 3, 3]) === false
+        @test insorted(2.5, R[1, 1, 2, 2, 3, 3]) === false
+
+        @test insorted(T(0), 1:3) === false
+        @test insorted(T(1), 1:3) == true
+        @test insorted(T(2), 1:3) == true
+        @test insorted(T(4), 1:3) === false
+
+        @test insorted(T(1), R(collect(1:10)), by=(x -> x >= 5)) == true
+        @test insorted(T(10), R(collect(1:10)), by=(x -> x >= 5)) == true
+    end
+
+    for (rg,I) in [(49:57,47:59), (1:2:17,-1:19), (-3:0.5:2,-5:.5:4)]
+        rg_r = reverse(rg)
+        rgv, rgv_r = collect(rg), collect(rg_r)
+        for i = I
+            @test insorted(i,rg) === insorted(i,rgv)
+            @test insorted(i,rg_r) === insorted(i,rgv_r,rev=true)
+        end
+    end
+
+    rg = 0.0:0.01:1.0
+    for i = 2:101
+        @test insorted(rg[i], rg) == true
+        @test insorted(prevfloat(rg[i]), rg) === false
+        @test insorted(nextfloat(rg[i]), rg) === false
+    end
+
+    rg_r = reverse(rg)
+    for i = 1:100
+        @test insorted(rg_r[i], rg_r) == true
+        @test insorted(prevfloat(rg_r[i]), rg_r) === false
+        @test insorted(nextfloat(rg_r[i]), rg_r) === false
+    end
+
+    @test insorted(1, 1:10) == insorted(1, collect(1:10), by=(x -> x >= 5))
+    @test insorted(10, 1:10) == insorted(10, collect(1:10), by=(x -> x >= 5))
+
+    @test insorted(0, []) === false
+    @test insorted(0, [1,2,3]) === false
+    @test insorted(4, [1,2,3]) === false
+    @test insorted(3, [10,8,6,9,4,7,2,5,3,1], by=(x -> iseven(x) ? x+5 : x), rev=true) === true
+end
 @testset "PartialQuickSort" begin
     a = rand(1:10000, 1000)
     # test PartialQuickSort only does a partial sort