Allow replacing with results of a function

src/abstractdataarray.jl

@@ -157,8 +157,13 @@ type EachReplaceNA{S, T}
     replacement::T
 end
 function each_replacena(da::AbstractDataArray, replacement::Any)
+  if isa(replacement, Function)
+    EachReplaceNAWithFunctionResult(da, replacement)
+  else
     EachReplaceNA(da, convert(eltype(da), replacement))
+  end
 end
+
 function each_replacena(replacement::Any)
     x -> each_replacena(x, replacement)
 end
@@ -167,4 +172,16 @@ Base.done(itr::EachReplaceNA, ind::Integer) = ind > length(itr.da)
 function Base.next(itr::EachReplaceNA, ind::Integer)
     item = isna(itr.da, ind) ? itr.replacement : itr.da[ind]
     (item, ind + 1)
-end
+end
+
+type EachReplaceNAWithFunctionResult{T}
+    da::AbstractDataArray{T}
+    f::Function
+end
+
+Base.start(itr::EachReplaceNAWithFunctionResult) = 1
+Base.done(itr::EachReplaceNAWithFunctionResult, ind::Int) = ind > length(itr.da)
+function Base.next(itr::EachReplaceNAWithFunctionResult, ind::Integer)
+  item = isna(itr.da, ind) ? itr.f(itr.da) : itr.da[ind]
+  (item, ind + 1)
+end

test/nas.jl

@@ -63,4 +63,9 @@ module TestNAs
     @test_throws NAException for v in each_failna(dv); end
     @test collect(each_dropna(dv)) == a
     @test collect(each_replacena(dv, 4)) == [4, 4, a..., 4]
+
+    dv = DataArray(Array(1:6), push!(fill(false, 3),fill(true, 3)...))
+    a = dropna(dv)
+    f = x -> round(Int, mean(dropna(x)))
+    @test collect(each_replacena(dv, f)) == [1, 2, 3, 2, 2, 2]
 end