add rand(::String)

JuliaLang · Jun 5, 2017 · 27d49ff · 27d49ff
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commit 27d49ff
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diff --git a/base/random.jl b/base/random.jl
@@ -257,7 +257,7 @@ 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
-* a `Dict`, a `Set` or an `IntSet`, or
+* an `AbstractString`, a `Dict`, a `Set` or an `IntSet`, 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;
@@ -683,6 +683,44 @@ end
 rand{T}(rng::AbstractRNG, r::AbstractArray{T}, dims::Dims) = rand!(rng, Array{T}(dims), r)
 rand(rng::AbstractRNG, r::AbstractArray, dims::Int...) = rand(rng, r, dims)
 
+# rand from a string
+
+rand(rng::AbstractRNG, s::AbstractString) = rand_iter(rng, s, Base.iteratorsize(s))
+rand(s::AbstractString) = rand(GLOBAL_RNG, s)
+
+## optimization for String
+
+isvalid_unsafe(s::String, i) = !Base.is_valid_continuation(unsafe_load(pointer(s), i))
+
+function rand(rng::AbstractRNG, s::String)
+    rg = Base.Random.RangeGenerator(1:s.len)
+    while true
+        pos = rand(Base.Random.GLOBAL_RNG, rg)
+        isvalid_unsafe(s, pos) && return s[pos]
+    end
+end
+
+## rand from an iterator
+
+rand_iter(rng, s, ::Base.IteratorSize) = throw(ArgumentError("iterator must have a known length"))
+
+function rand_iter(rng::AbstractRNG, s, ::Union{Base.HasShape,Base.HasLength})::eltype(s)
+    pos = rand(rng, 1:length(s))
+    for (i, c) in enumerate(s)
+        i == pos && return c
+    end
+end
+
+## 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)

diff --git a/test/random.jl b/test/random.jl
@@ -313,7 +313,9 @@ for rng in ([], [MersenneTwister(0)], [RandomDevice()])
                    (Set(rand(Int, 20)), Int),
                    (Dict(zip(rand(Int,10), rand(Int, 10))), Pair{Int,Int}),
                    (1:100, Int),
-                   (rand(Int, 100), Int)]
+                   (rand(Int, 100), Int),
+                   ("qwèrtï", Char),
+                   (Base.Test.GenericString("qwèrtï"), Char)]
     b2 = big(2)
     u3 = UInt(3)
     for f in [rand, randn, randexp]
@@ -339,9 +341,12 @@ 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..., Array{T}(5), C)    ::Vector{T}
-        a4 = rand!(rng..., Array{T}(2, 3), C) ::Array{T, 2}
-        for a in [a0, a1..., a2..., a3..., a4...]
+        a3 = rand(rng..., C, (2, 3))          ::Array{T, 2}
+        a4 = rand!(rng..., Array{T}(5), C)    ::Vector{T}
+        a5 = 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...]
             @test a in C
         end
     end