added extrema(A,dims)

base/docs/helpdb/Base.jl

@@ -2083,11 +2083,18 @@ appended to an internal buffer of backtraces.
 :@profile
 
 """
-    extrema(itr)
+    extrema(itr) -> Tuple
 
 Compute both the minimum and maximum element in a single pass, and return them as a 2-tuple.
 """
-extrema
+extrema(itr)
+
+"""
+    extrema(A,dims) -> Array{Tuple}
+
+Compute the minimum and maximum elements of an array over the given dimensions.
+"""
+extrema(A,dims)
 
 """
     isdigit(c::Union{Char,AbstractString}) -> Bool

base/reduce.jl

@@ -353,6 +353,38 @@ function extrema(itr)
     return (vmin, vmax)
 end
 
+function extrema(A::AbstractArray, dims)
+    sz = [size(A)...]
+    sz[[dims...]] = 1
+    B = Array{Tuple{eltype(A),eltype(A)}}(sz...)
+    extrema_cartesian!(B, A)
+end
+
+@generated function extrema!{T,N}(B, A::Array{T,N})
+    quote
+        sA = size(A)
+        sB = size(B)
+        @nloops $N i B begin
+            AI = @nref $N A i
+            (@nref $N B i) = (AI, AI)
+        end
+        Bmax = sB
+        Istart = ones(Int,ndims(A))
+        Istart[([sB...].==1) & ([sA...].!=1)] = 2
+        @inbounds @nloops $N i d->(Istart[d]:size(A,d)) begin
+            AI = @nref $N A i
+            @nexprs $N d->(j_d = min(Bmax[d], i_{d}))
+            BJ = @nref $N B j
+            if AI < BJ[1]
+              (@nref $N B j) = (AI, BJ[2])
+            elseif AI > BJ[2]
+              (@nref $N B j) = (BJ[1], AI)
+            end
+        end
+        squeeze(B, tuple(find([sB...].==1)...))
+    end
+end
+
 ## all & any
 
 any(itr) = any(IdFun(), itr)

test/reduce.jl

@@ -167,6 +167,9 @@ prod2(itr) = invoke(prod, Tuple{Any}, itr)
 @test maximum(collect(Int16(1):Int16(100))) === Int16(100)
 @test maximum(Int32[1,2]) === Int32(2)
 
+@test extrema_cartesian([1 2 3; 4 5 6; 7 8 9], 1) == [(1,7),(2,8),(3,9)]
+@test extrema_cartesian([1 2 3; 4 5 6; 7 8 9], 2) == [(1,3),(4,6),(7,9)]
+
 # any & all
 
 @test any(Bool[]) == false