add rand(::String) (#22224)

NEWS.md

@@ -53,6 +53,9 @@ Library improvements
   * The function `randn` now accepts complex arguments (`Complex{T <: AbstractFloat}`)
     ([#21973]).
 
+  * The function `rand` can now pick up random elements from strings, associatives
+    and sets ([#22228], [#21960], [#18155], [#22224]).
+
   * Method lists are now printed as a numbered list. In addition, the source code of a
     method can be opened in an editor by entering the corresponding number in the REPL
     and pressing `^Q` ([#22007]).
@@ -749,6 +752,7 @@ Command-line option changes
 [#17785]: https://github.com/JuliaLang/julia/issues/17785
 [#18012]: https://github.com/JuliaLang/julia/issues/18012
 [#18050]: https://github.com/JuliaLang/julia/issues/18050
+[#18155]: https://github.com/JuliaLang/julia/issues/18155
 [#18159]: https://github.com/JuliaLang/julia/issues/18159
 [#18218]: https://github.com/JuliaLang/julia/issues/18218
 [#18251]: https://github.com/JuliaLang/julia/issues/18251
@@ -882,6 +886,7 @@ Command-line option changes
 [#21759]: https://github.com/JuliaLang/julia/issues/21759
 [#21818]: https://github.com/JuliaLang/julia/issues/21818
 [#21825]: https://github.com/JuliaLang/julia/issues/21825
+[#21960]: https://github.com/JuliaLang/julia/issues/21960
 [#21973]: https://github.com/JuliaLang/julia/issues/21973
 [#21974]: https://github.com/JuliaLang/julia/issues/21974
 [#22007]: https://github.com/JuliaLang/julia/issues/22007
@@ -890,3 +895,7 @@ Command-line option changes
 [#22064]: https://github.com/JuliaLang/julia/issues/22064
 [#22187]: https://github.com/JuliaLang/julia/issues/22187
 [#22188]: https://github.com/JuliaLang/julia/issues/22188
+[#22224]: https://github.com/JuliaLang/julia/issues/22224
+[#22228]: https://github.com/JuliaLang/julia/issues/22228
+[#22245]: https://github.com/JuliaLang/julia/issues/22245
+[#22310]: https://github.com/JuliaLang/julia/issues/22310

base/random.jl

@@ -256,8 +256,9 @@ globalRNG() = GLOBAL_RNG
 
 Pick a random element or array of random elements from the set of values specified by `S`; `S` can be
 
-* an indexable collection (for example `1:n` or `['x','y','z']`), or
-* an `Associative` or `AbstractSet` object, or
+* an indexable collection (for example `1:n` or `['x','y','z']`),
+* an `Associative` or `AbstractSet` object,
+* a string (considered as a collection of characters), or
 * a type: the set of values to pick from is then equivalent to `typemin(S):typemax(S)` for
   integers (this is not applicable to [`BigInt`](@ref)), and to ``[0, 1)`` for floating
   point numbers;
@@ -709,6 +710,33 @@ end
 rand(rng::AbstractRNG, r::AbstractArray{T}, dims::Dims) where {T} = rand!(rng, Array{T}(dims), r)
 rand(rng::AbstractRNG, r::AbstractArray, dims::Integer...) = rand(rng, r, convert(Dims, dims))
 
+# rand from a string
+
+isvalid_unsafe(s::String, i) = !Base.is_valid_continuation(unsafe_load(pointer(s), i))
+isvalid_unsafe(s::AbstractString, i) = isvalid(s, i)
+_endof(s::String) = s.len
+_endof(s::AbstractString) = endof(s)
+
+function rand(rng::AbstractRNG, s::AbstractString)::Char
+    g = RangeGenerator(1:_endof(s))
+    while true
+        pos = rand(rng, g)
+        isvalid_unsafe(s, pos) && return s[pos]
+    end
+end
+
+rand(s::AbstractString) = rand(GLOBAL_RNG, s)
+
+## rand from a string for arrays
+# we use collect(str), which is most of the time more efficient than specialized methods
+# (except maybe for very small arrays)
+rand!(rng::AbstractRNG, A::AbstractArray, str::AbstractString) = rand!(rng, A, collect(str))
+rand!(A::AbstractArray, str::AbstractString) = rand!(GLOBAL_RNG, A, str)
+rand(rng::AbstractRNG, str::AbstractString, dims::Dims) = rand!(rng, Array{eltype(str)}(dims), str)
+rand(rng::AbstractRNG, str::AbstractString, d1::Integer, dims::Integer...) = rand(rng, str, convert(Dims, tuple(d1, dims...)))
+rand(str::AbstractString, dims::Dims) = rand(GLOBAL_RNG, str, dims)
+rand(str::AbstractString, d1::Integer, dims::Integer...) = rand(GLOBAL_RNG, str, d1, dims...)
+
 ## random BitArrays (AbstractRNG)
 
 function rand!(rng::AbstractRNG, B::BitArray)

test/random.jl

@@ -319,8 +319,9 @@ for rng in ([], [MersenneTwister(0)], [RandomDevice()])
                    1:100                   => Int,
                    rand(Int, 100)          => Int,
                    Int                     => Int,
-                   Float64                 => Float64]
-
+                   Float64                 => Float64,
+                   "qwèrtï"                => Char,
+                   GenericString("qwèrtï") => Char]
     b2 = big(2)
     u3 = UInt(3)
     for f in [rand, randn, randexp]
@@ -346,10 +347,13 @@ for rng in ([], [MersenneTwister(0)], [RandomDevice()])
         a0 = rand(rng..., C)                  ::T
         a1 = rand(rng..., C, 5)               ::Vector{T}
         a2 = rand(rng..., C, 2, 3)            ::Array{T, 2}
-        a3 = rand(rng..., C, b2, u3)          ::Array{T, 2}
-        a4 = rand!(rng..., Array{T}(5), C)    ::Vector{T}
-        a5 = rand!(rng..., Array{T}(2, 3), C) ::Array{T, 2}
-        for a in [a0, a1..., a2..., a3..., a4..., a5...]
+        a3 = rand(rng..., C, (2, 3))          ::Array{T, 2}
+        a4 = rand(rng..., C, b2, u3)          ::Array{T, 2}
+        a5 = rand!(rng..., Array{T}(5), C)    ::Vector{T}
+        a6 = rand!(rng..., Array{T}(2, 3), C) ::Array{T, 2}
+        @test size(a1) == (5,)
+        @test size(a2) == size(a3) == (2, 3)
+        for a in [a0, a1..., a2..., a3..., a4..., a5..., a6...]
             if C isa Type
                 @test a isa C
             else
@@ -358,7 +362,8 @@ for rng in ([], [MersenneTwister(0)], [RandomDevice()])
         end
     end
     for C in [1:0, Dict(), Set(), IntSet(), Int[],
-              GenericDict(Dict()), GenericSet(Set())]
+              GenericDict(Dict()), GenericSet(Set()),
+              "", Base.Test.GenericString("")]
         @test_throws ArgumentError rand(rng..., C)
         @test_throws ArgumentError rand(rng..., C, 5)
     end