WIP: Added 'order' keyword argument to cartesian product

README.md

@@ -152,9 +152,9 @@ Install this package with `Pkg.add("Iterators")`
     i = 'c'
     ```
 
-- **product**(xs...)
+- **product**(xs..., [order])
 
-    Iterate over all combinations in the cartesian product of the inputs.
+    Iterate over all combinations in the cartesian product of the inputs. The `order` keyword argument specifies whether the elements are traversed in lexicographic order (`false`) or anti-lexicographic order (`true`, the default value).
 
     Example:
     ```julia
@@ -171,6 +171,21 @@ Install this package with `Pkg.add("Iterators")`
     p = (2,2)
     p = (3,2)
     ```
+    while
+    ```julia
+    for p in product(1:3,1:2,order=false)
+        @show p
+    end
+    ```
+    yields
+    ```
+    p = (1,1)
+    p = (1,2)
+    p = (2,1)
+    p = (2,2)
+    p = (3,1)
+    p = (3,2)
+    ```
 
 
 - **distinct**(xs)

src/Iterators.jl

@@ -19,7 +19,9 @@ export
     imap,
     subsets,
     iterate,
-    @itr
+    @itr,
+    AntiLexicographicOrder,
+    LexicographicOrder
 
 # Infinite counting
 
@@ -258,17 +260,30 @@ done(it::Chain, state) = state[1] > length(it.xss)
 
 # Cartesian product as a sequence of tuples
 
-immutable Product
+abstract SortingOrder
+
+abstract LexicographicOrder <: SortingOrder
+abstract AntiLexicographicOrder <: SortingOrder
+
+immutable Product{order}
     xss::Vector{Any}
-    function Product(xss...)
-        new(Any[xss...])
-    end
+    Product(xss...)=new(Any[xss...])
 end
 
+
 eltype(p::Product) = tuple(map(eltype, p.xss)...)
 length(p::Product) = prod(map(length, p.xss))
 
-product(xss...) = Product(xss...)
+function product(xss...; order=AntiLexicographicOrder)
+  if order==AntiLexicographicOrder
+    Product{order}(xss...)
+  elseif order==LexicographicOrder
+    Product{order}(reverse(xss)...)
+  else
+    error("Order '$(order)' unsupported")
+    Product{order}(xss...)
+  end
+end
 
 function start(it::Product)
     n = length(it.xss)
@@ -288,10 +303,16 @@ function start(it::Product)
     return js, vs
 end
 
-function next(it::Product, state)
+function next{T}(it::Product{T}, state)
     js = copy(state[1])
     vs = copy(state[2])
-    ans = tuple(vs...)
+    ans = if T==AntiLexicographicOrder
+             tuple(vs...)
+          elseif T==LexicographicOrder
+             tuple(reverse(vs)...)
+          else
+             error("Ordering '$(T)' not supported")
+          end 
 
     n = length(it.xss)
     for i in 1:n

test/runtests.jl

@@ -94,6 +94,8 @@ x1 = 1:2:10
 x2 = 1:5
 @test collect(product(x1, x2)) == vec([(y1, y2) for y1 in x1, y2 in x2])
 
+@test collect(product(x1, x2, order=LexicographicOrder)) == vec([(y1, y2) for y2 in x2, y1 in x1])
+
 # distinct
 # --------