WIP/ RFC/First PR: Add unzip to base.iterators.jl

base/iterators.jl

@@ -200,7 +200,7 @@ end
 For a set of iterable objects, returns an iterable of tuples, where the `i`th tuple contains
 the `i`th component of each input iterable.
 
-Note that [`zip`](@ref) is its own inverse: `collect(zip(zip(a...)...)) == collect(a)`.
+Note that the inverse of [`zip`](@ref) is [`unzip`](@ref).
 
 ```jldoctest
 julia> a = 1:5
@@ -240,6 +240,32 @@ end
 iteratorsize{I1,I2}(::Type{Zip{I1,I2}}) = zip_iteratorsize(iteratorsize(I1),iteratorsize(I2))
 iteratoreltype{I1,I2}(::Type{Zip{I1,I2}}) = and_iteratoreltype(iteratoreltype(I1),iteratoreltype(I2))
 
+# unzip
+```jldoctest
+
+For iterable objects of the same length, returns iterable sets, where the ith set contains
+the ith component of each input iterable object.
+
+Note that the inverse of [`unzip`](@ref) is [`zip`](@ref).
+
+julia>  z = [[1,"a",:meow], [2,"b",:woof], [3,"c",:doh!]]
+3-element Array{Array{Any,1},1}:
+Any[1, "a", :meow]
+Any[2, "b", :woof]
+Any[3, "c", :doh!]
+
+julia> unzip(z)
+Array{Int64,1}:[1,2,3]
+Array{String,1}["a","b","c"]
+Array{Symbol,1}[:meow,:woof,:doh!]
+```
+unzip(iter::AbstractZipIterator) = _unzip(iter)
+# This avoids exporting the method that isn't for AbstractZipIterators
+_unzip(iter::Zip1) = (iter.a,)
+_unzip(iter::Zip2) = (iter.a, iter.b)
+_unzip(iter::Zip) = (iter.a, unzip(iter.z)...)
+_unzip(iter) = (iter,)
+
 # filter
 
 struct Filter{F,I}

test/iterators.jl

@@ -22,6 +22,22 @@ let z = zip(1:2, 3:4, 5:6)
     @test eltype(z) == Tuple{Int,Int,Int}
 end
 
+# unzip
+let z = zip(1:2)
+    @test unzip(z) == 1:2
+    @test eltype(unzip(z)) == UnitRange{Int64}
+end
+
+let z = zip(1:2, 3:4)
+    @test collect(unzip(z)) == [(1,2), (3,4)]
+    @test eltype(unzip(z)) == UnitRange{Int64}
+end
+
+let z = zip(1:2, 3:4, 5:6)
+    @test collect(unzip(z)) == [(1,2), (3,4), (5,6)]
+    @test eltype(unzip(z)) == UnitRange{Int64}
+end
+
 @test eltype(Iterators.filter(isodd, 1:5)) == Int
 
 # typed `collect`